My friend's PC is getting a black screen with "Operating System Not Found". I asked him if he had done anything to the PC. He said the only thing he has done is turn it off and on. I assumed the hdd was smoked because the BIOS wouldnt see it. Try to use a bootable and run FDISK but no hard drive was found. After turning it on and off a few times it came back on its own. Weird. However, he turned it off and the next morning same problem, the black screen. I am not sure if it would be a power supply issue since it did come back to life once. Maybe the hard drive just kicked the bucket and he needs a new one. Any advice would be much appreciated. Thanks.

It sounds like his BIOS is set to automatically detect IDE drives every time it boots, I suggest you enter BIOS and change it so that every IDE drive is defined (you can just choose AUTO DETECT and it should fill the information in for you). This might fix the problem. I would also suggest opening the case and checking that both the power plug and the data cable are connected firmly to the hard drive (also check that the data cable is connected frimly to the motherboard). If the above dosen't work see if you can try another hard drive (that you already have) in the PC, see if it does the same thing with that hard drive and if it dosen't then you know that your friend's hard drive is bad and needs to be replaced.