PC turns off after a few seconds

[infernoAUS]

Specs:
CPU: i5 760
GPU: GTX 580
PSU: Corsair 750W
RAM: 2 x 4GB 1333
Motherboard: Gigabyte GA-P55A-UD3

I bought this second hand on Sunday but started running it yesterday, it was fine all day but today I opened it up and cleaned it out with compressed air, and now it shuts off when it gets to OS. All I did was clean the fans and reinstalled the CPU cooler. What could I have done to cause this? I'd find it unlikely that a problem just appeared which isn't related to me opening it up... Please help me out!
Thanks

 

[dency45]

recheck the connections of the PSU to the motherboard. Or it could be the power supply is dead.

not sure, im just trying to help.

 

[cumi2k4]

probably you did not apply thermalpaste on the cpu cooler correctly? have you try monitoring cpu temp on the bios?

 

[infernoAUS]

CPU was 89°C in BIOS. When I tried to go into it again it shut down before I could look. I guess this is definitely the cause then? I'll have to get some thermal paste, but I don't see how just taking the cooler off caused this

edit: Actually that temp can't be right, it hasn't changed at all each time (always 89.0) and the heatsink doesn't feel hot

 

[cumi2k4]

did you put the cooler without applying new thermal paste? you need to put a new one each time you take it off.
89 degree celcius is quite hot, no wonder your pc perform automatic shutdown, it is designed to do so to prevent your processor burning out. your heatsink might not feel hot, due to lack of good thermal conductor from the processor to the heatsink...that might be the cause.

 

[infernoAUS]

Okay thanks, I'm getting the necessary materials tomorrow and I'll report back!

 

[chugot9218]

Anytime you remove the heatsink you must replace the thermal paste, and also, when you are using compressed air to clean your fans stick a toothpick or something non-conducive in the blades so they do not spin, the compressed air can actually make them spin faster than they are designed to and damage them.

 

[infernoAUS]

Thank you guys so much for the replies! Cleaned the old thermal paste and reinstalled and it's working great, temps are good too.

 

[infernoAUS]

Best answer selected by infernoAUS.