It made a buzz sound, not like the beep I heard on my last computer which was more like a miniature bullhorn just before it crashed, but it was a buzz sound and then a blue screen with words in white LETTERS, then it restarts and windows says its recovered from a SPONTANEOUS shut down. It's up and running again, but I'm worried. The last computer I had did something similar and there was no reviving it after that. It is a desktop compaq presario SR5210NX Processor intel celeron processor 420, but a friend of ours who runs a computer repair shop takes unwanted computers, FIXES them if worth salvaging, and sells them from time to time. We've known him for years so I don't think he'd knowingly sell us junk, but we've had this for about two months now. What could be wrong?Need to find the location of the buzzing sound. This can be a failing hard drive, power supply, or a fan that has bearings that occasionally make a buzzing sound and can cause blue screen if an over temp condition is reached with say a video card. 

I'd run this past your friend who sold you it FIRST to make sure that opening or tampering with the computer will not void any warranty if he gave you one. He might also be willing to look it over for you and supply replacement parts for free like I do for my friends when parts that didnt cost me anything are available to give away.

But to locate the noise, I'd pop the case open and run it with the side panel off and when the buzz sound happens again try to pinpoint its location. I am thinking that its either a Power Supply or a Video Card with a fan thats bearings are shot on and making the buzzing noise.

Also its important to know if the buzzing noise is COMING from inside the computer or through the Speakers of the computer. As for I have seen bad RAM cause the sound card to output a buzz right before a blue screen and then reboot.