Internal hard disk drive not found. To resolve this issue, try to reseat the drive. No bootable devices--strike F1 to retry boot, F2 enter Setup Menu, F5 enter PSA.   How do I fix this problem?
My computer no longer boots Windows or the installed operating system. Instead, I may get this error:  PXE-E61: Media test failure, check cable -or- Check cable connection!  PXE-M0F: Exiting PXE ROM.   and/or one of the following messages or similar:  Operating System not found  No boot device available- No bootable devices--strike F1 to retry boot, F2 for setup utility  No bootable device -- insert boot disk and press any key  No Boot Device Found. Press any key to reboot the machine  Default Boot Device Missing or Boot Failed  Reboot and Select proper Boot device or Insert Boot Media in selected Boot device   What does this mean and what can I do?     This question comes up often and the answers are usually the same. This post is meant to provide a definitive, canonical answer for this problem. Feel free to edit the answer to add additional details.
Why is there no 32 bit ISO for the new Ubuntu 18.04? Cartoon TV Show About Three Kids and Monsters and a "veil" between realms In the Futurama episode "" they save the world by rotating the Earth backwards saying it shouldn't matter (which direction Earth rotates). If Earth rotated clockwise and remained in it's current counter-clockwise orbit around the Sun, would it affect anything beyond the direction the constellations move across the sky? Arrays in Unix Bourne Shell I am trying to use arrays in Bourne shell (/bin/sh). I found that the way to initialize array elements is:  arr=(1 2 3)   But it is encountering an error:  syntax error at line 8: `arr=' unexpected   Now the post where I found this syntax says it is for bash, but I could not find any separate syntax for Bourne shell. Does the syntax stand the same for /bin/sh as well? I have a bunch of raw data values that are dollar amounts and I want to find a confidence interval for a percentile of that data.  Is there a formula for such a confidence interval? Meta duplicates don't require an answer. Don't suggest there is one when that's not true Prove that $2^{1/2}$ is irrational I'm trying to understand each part of this completed proof that my professor did, here is my interpretation in parentheses, please advise as necessary.  Proof: Assume that $2^{1/2}$ is rational, then $2^{1/2}$ = $p/q$ for some integer $p$ and $q$ with $q \neq 0$ and $\gcd(p,q) = 1$  $$(p/q)^2 = 2 = p^2 / q^2 $$ $$\text{ (What was the purpose of squaring √2 and p/q?)}$$  $$p^2 = 2q^2$$ $$ \text{ (Is this basically just canceling out the q^2 on left side, and multiplying the right side?)}$$  2 | p^2 => (2 divides p^2 since it is a factor)  2 | p => (thus 2 divides p)  p = 2k for some integer k => (definition of even)  (2k)^2 = 4k^2 = 2q^2 => (Why are we squaring 2k, and how does 4k^2 = 2q^2?)   q^2 = 2k^2 => (Canceled out 2 on one side, and dividing on other)  2 | q^2 => (2 divides q^2)  2 | q => (thus 2 divides q)  2 | gcd(p,q) => (2 divides gcd of p and q)  2 | 1 Which is a Contradiction (no clue how I got here) I have just finished my undergraduate studies. During last two semesters I've taken two subjects dealing with manifolds:   Analysis on manifolds, containing: definition of manifold, tangent space (as derivations and classes of curves), vector fields, vector bundles, flows, Lie derivatives, integration on manifolds (Stokes theorem), forms, Hodge decomposition theorem Introduction to differential geometry (for me it should be called introduction to Riemannian manifolds) containing: tensor calculus introduction, Riemannian manifold definition, connections, curvatures, geodesic, normal coordinates, geodesic completness theorem, classification throught curvature, jacobi fields, harmonic maps.    Now, for me differential geometry was/is a theory about manifolds, so anything dealing with manifolds is branch of differential geometry. On the other hand I am preparing for taking part in local conference called: "algebraic and differential topology".  I have read: ,  ,  , yet I still don't really know if differential topology is subtheory of differential geometry or is it seperate theory and how is it located between differential geometry and algebraic topology. For example I expect that studies on Riemmanian manifolds are part of differential geometry but would problem of classification manifolds up to diffeomorphism be a part of differential topology or geometry ?  Request: I would be grateful for your characterisation of differential topology and differential geometry possibly with examples of problems, theorems present at them. "Awesome" vs. "Awful" One or more of the following things happened to me on a Stack Exchange site:   My post(s) were wrongly deleted or locked by a moderator A moderator posted a wrong comment on one of my posts I was suspended, but did not do anything wrong I asked a meta question, but the question was closed and/or deleted A moderator discredited me in public ...   I think a moderator has abused their power, but I feel powerless against them.  What recourse do I have now? What can I do when I feel that a moderator has abused their power, and has been repeatedly unfair in their dealings with me? Pass by Reference / Value in C++ I would like to clarify the differences between by value and by reference.  I drew a picture     So, for passing by value,  a copy of an identical object is created with a different reference, and the local variable is assigned the new reference, so to point to the new copy  How to understand the words: " If the function modifies that value, the modifications appear also within the scope of the calling function for both passing by value and by reference "  Thanks! Replace non-numeric with empty string I was looking for a possible duplicated question about  in , then looked using the Big G! since the integrated search didn't give me any useful result (laugs) then I found the , but in Stackoverflow! Then, I proceed to flag as off-topic, but since "It's too old to migrate" I don't have the option to do so...  So, my question is, should I leave it like that? Or the question is better in UL (also on topic, just read the question)? Any guidance to this young pada-wan is greatly appreciated. Searching for words in question titles I'm trying to search for questions that have specific words in their titles using the  search feature, but it seems that it does not return any search results.  Using this feature, I tried to search for questions on Stack Overflow with , but this search query returns no results.  Is it still possible to filter the search results based on words in question titles? Underfull \hbox in bibliography I am getting lots of "Underfull \hbox" warnings that point to the *.bbl file. It looks like these messages appear only when URLs are very long, like in the below example:  @techreport{nistguidesec,   author    = {Wayne Jansen and Timothy Grance},   title     = {Guidelines on Security and Privacy in Public Cloud Computing},   month    = {January},   note     = {Draft Special Publication 800-144. Available at \url{http://csrc.nist.gov/publications/drafts/800-144/Draft-SP-800-144_cloud-computing.pdf}}, }   In the produced PDF text is correctly hyphened and links are correctly split over several lines (I am using hyperref package)  How can I avoid annoying warning messages about "underfull \hbox" pointing to bibliography? how to execute mongo admin command from java Electromagnetic waves in vacuum If there is no source then also there is electromagnetic waves described by Maxwell equation. how if there is no source then existence of EM waves. What gives energy to this EM  waves. Is it vacuum fluctuation or something else? Bag-of-Words for Text Classification: Why not just use word frequencies instead of TFIDF? A common approach to text classification is to train a classifier off of a 'bag-of-words'. The user takes the text to be classified and counts the frequencies of the words in each object, followed by some sort of trimming to keep the resulting matrix of a manageable size.  Often, I see users construct their feature vector using TFIDF.  In other words, the text frequencies noted above are down-weighted by the frequency of the words in corpus.  I see why TFIDF would be useful for selecting the 'most distinguishing' words of a given document for, say, display to a human analyst.  But in the case of text categorization using standard supervised ML techniques, why bother downweighting by the frequency of documents in the corpus?  Will not the learner itself decide the importance to assign to each word/combination of words?  I'd be grateful for your thoughts on what value the IDF adds, if any. I have a production server running with the following flag: -XX:+HeapDumpOnOutOfMemoryError  Last night it generated a java-38942.hprof file when our server encountered a heap error. It turns out that the developers of the system knew of the flag but no way to get any useful information from it.  Any ideas? How do tag merge requests work? I had raised a  to merge pre-build-event, and pre-buildevent; and postbuild-event and post-build-event. That was about 11 months ago, and I still see these two tags even now.  How are tag merge requests handled? Is there a better way for tag merge requests other than posting on Meta?