I have a Lenovo tower PC. I had left it powered up last night. When I got up this morning, there were error messages indicating hard drive problems. It would not shut down normally, so I had to push and hold the power button until it powered off. Powered it back on and got the dreaded "Operating System Not Found" message! I fiddled with it for a bit, but had to get ready for work. When I got home tonight, I tried booting up several times with the same results. At one point, I vibrated the tower (a well-calibrated "THUMP", actually), then tried to boot. To my amazement, I saw a "configuration changed" message, and it eventually came up. Quickly, I moved all of the files I wanted to save to a USB key. Got that done, then shut down. Tried to boot again, got absolutely nothing. I powered it off, got into the case, and made sure everything was seated good, and reseated the memory DIMMs. I took the CPU fan off of the heat sink and cleaned both. Tried to get the heat sink off of the CPU chip, but couldn't figure out how to separate the two. Tried to power up, and it acted worse than before...... power light would flash, but the tower would not come to life at all. Went online and found a Hardware Maintenance Manual for the PC, and figured out how to unlatch the heat sink from the CPU chip. I took it all apart, reseated everything again, I tried to take the heat sink off of the CPU chip. The chip came off with the heat sink, which it should not do! Fortunately, the pins of the chip were not damaged. I gently pried the chip off of the heat sink (stuck on tightly with heat conducting compound), then reseated the chip into it's holder, reattached the heat sink (applied new heat conducting compound) and cooling fan, and powered up. Came up like a charm!!!! Boy, was I relieved!!!!
I have a Ubuntu operating system. When it came up, I ran all of the tests that were available, including CPU, memory , and hard drive tests. All were good. I was especially glad to see that the SMART info for the hard drive indicated a well-functioning hard drive!!
Back in business, finally! (All of this was during the canning of 7 quarts of green beans!!!!)