PC turn off itself even though in BIOS menu

[coalchamber]

My PC just turn on for 3 second after I cleaning a dust from my PC, even when I open BIOS setting. what can possibly cause the problem ?
wrong mounted Heatsink Fan?
Motherboard, HDD or anything else ?
my PC is beeping from the start which is normal (some people ask me if my PC beeping or not)

 

[rgd1101]

did you unplug anything when you cleaning?

 

[coalchamber]

did you unplug anything when you cleaning?

yes, Heatsink fan and case fan, but I mounted it on the right place. are they have a connection for this problem ?

 

[rgd1101]

yes, it sound like it the cpu is overheating.

 

[coalchamber]

yes, it sound like it the cpu is overheating.

can it overheating even though I just starting my PC ?

 

[Y0GI]

can it overheating even though I just starting my PC ?

Yes! Definitely!

Yogi