After applying thermal paste,now computer beeps & shuts down all of su

My desktop was shutting down because of thermal event. I cleaned everything, applied new thermal paste, after that re installed windows but still it beeps when booting and shuts down all of a sudden. Occasionally it worked for an hour or so flawlessly. If it is again because of overheating it should shut down after 5 minutes or so when it heats up not when starting it in morning (after keeping it shut overnight). It shuts down even before booting. thanks for all of the help.

Don`t know who told you it will take 5 minutes, A pc can shut down in less then 30 seconds if the cpu goes over the temprature limit. It supposed to do that.

If you can get it to POST go into the BIOS and there should be a page that shows you your temps and fan speeds. Booting into the BIOS screen should put next to no load on your system and maybe give you a chance to see what your CPU temp is.

How much thermal past did you apply?
Heatsink mounted correctly?
CPU fan plugged back in?

It is possible that your CPU is already damaged from overheating. That can setup a condition known as thermal runaway. Thermal runaway - Wikipedia, the free encyclopedia

alphanumeric said:

If you can get it to POST go into the BIOS and there should be a page that shows you your temps and fan speeds. Booting into the BIOS screen should put next to no load on your system and maybe give you a chance to see what your CPU temp is.

How much thermal past did you apply?
Heatsink mounted correctly?
CPU fan plugged back in?

It is possible that your CPU is already damaged from overheating. That can setup a condition known as thermal runaway. Thermal runaway - Wikipedia, the free encyclopedia

I applied pea size thermal paste but didn't spread it but put the heat sink over it and screwed it, heat sink I think is mounted correctly as I could tighten the screws. I plugged back fan too. I went to BIOS but computer again shut down after a short time. I restarted it and this time let it restart normally and then I saw the message that cpu was shut down due to thermal event. Does it mean that CPU is still OK? thanks

Layback Bear said:

Make sure on boot your cpu heat sink fan comes on at full speed. As has been stated before, bios puts very little load on the system their for should create very little heat.

I feel as fan runs slow, However I could go to BIOS > event viewer and saw Processor Thermal trip with 27 in parenthesis in front of it. I don't know how to make fan run at full speed.