What specifically failed in the system unit?

Question

Iron

There is a rather old system unit (manufactured in 2007), which has been repeatedly repaired (the power supply unit, the disk drive have been changed). Came with Windows Vista, changed systems several times, there were 7 and 8, but in the end, it was restored to the original OS from the recovery disk. The second operating system is Ubuntu 14.04.
The system unit was usually turned off only to clean it. About a couple of weeks ago, a rather strong noise began during preloads, which stopped after the systems were fully loaded (win / ub). I thought that it was time to clean it again, but it didn’t come to cleaning, because a couple of days ago it just flew into a blue screen and began to freeze tightly 1-2 minutes after turning it on, and sometimes even during loading any of the installed systems. At the same time, it was not always possible to get a signal to the monitor, it can start 3-4 times at idle - the system unit starts up, the coolers work, there is no signal to the monitor and other devices. Then, after 2-3 power-ups, it suddenly appears, but then the system just hangs. We managed to figure out the noise, it really was due to dust in the cooler under the motherboard. But what's the point then?

Answer 1

At a minimum, an audit of electrolytic capacitors is needed for swelling in the PSU and on the MP.

Answer 2

Check if the speaker is connected to the motherboard. Remove the RAM from the slot(s). Turn on your computer. Are there any sounds? If not, something with the processor (unlikely), or with the power of the processor. In this case, carefully inspect the elements next to the socket. Since the computer still sometimes turns on, the power keys are working. Most likely, as mentioned above, the failure of the capacitors in the processor power circuit, visually this is manifested by "swelling". But if nothing is visually visible, the capacitors may still be inoperative.
If there is a squeak, then check the video card and the south bridge. In this case, I would check the power supply last.