Computer shuts down 2 seconds after startup, what could be wrong?

Question

Iron

Computer shuts down 2 seconds after being turned on. After a while, everything turns on normally. This can happen in a day or a month. What could be the problem?
Mother ASRock g41m-s3, RAM 8 gb, gtx 750-ti, Xeon e5450, PSU atx-500h, motherboard and PSU are very old, other components changed in the range of 1-2 years. Maybe the PSU is not pulling, or is it simply dying?
It also happens that the computer turns on, Windows appears, loads and bam - freezes. The computer itself works, but the picture on the screen freezes, only reboot saves. I'm already starting to think. Confused in short.

Answer 1

Test components one at a time or replace with a known good one.
No, well, what do you want with such meager data, especially since you yourself guess "what can be" - it remains to verify this experimentally, and no one can do this for you. And if you believe in fortune-telling on the Internet - I have bad news for you :D
Okay. In old power supplies, a common problem is the "drying" of capacitors, they just need to be replaced and it will last another 3-5-7 years, depending on the quality of the installed capacitors.

Answer 2

Change PSU

Answer 3

I would start by checking the PSU. Conders are already tired of the campaign.

Answer 4

Weird. In general, I disconnected the DVD drive and the card reader and everything worked. I doubt they were broken. Most likely, the PSU simply took off the load and the system turned on quietly. :/