Its an office pc, so i'll drop as much info as i canWe're going to need more info.
When posting a thread of troubleshooting nature, it's customary to include your full system's specs. List them like so:
How old is your PSU? What was the last thing you were doing on your PC before the issue cropped up?
Fans were working fine, i used to clean it every now and then, but never replaced the thermal paste.It probably got too hot. CPU is from 2007, even if it got purchased in 2010 or something. How often was it maintained? cleaning dust, applying new paste, checking fan spin, etc.?
Ok so i removed one ram stick and it started working, guess that stick causing all the troubleIf it now won't even POST, probably liittle worry about overheating, but, for sure thermal paste on a heatsink does not last forever. You can try a new BIOS battery for $3, perhaps slave in a known good PSU to rule that out, test with one stick of RAM alternately, eventually leaving you only with the mainboard (once you remove/disconnect everything else ruling out other potential causes. (a mainboard failure is 10-20x more likely than an actual 'out of the blue' true hard cpu failure...