Who ever knows a lot about computers, please help me (Hlymzik...you're one of them... xD)

Recently, my computer started reseting a lot, and I don't know why, I do believe it's the virus that's causing the problem or could be that my computer has too many Spywares or rogue programs on them.

I need help, my computer usually resets when I hear my computer make a "Krrrzzzt...." sound and when it resets it goes "Pffsss...." and it's silent and when it switches on I hear "Tiiik!".

On other events like when the H.D.D (The light near the switch on button and near the "Power" light) shines bright red, then the computer resets.

Please, could anyone help me?

Could you answer to those questions? :

How long it work before it turns off?

How long it work when you turn it on immediatly after shut down?

Do there comes any message before shutting down?

How old is your comp?

When you were cleaning inside of case last time?

Do there comes only one Piiip signal or few ?

My ocmputer is about 2~3 years old and it shuts down whenever I have too many programs running and when the computer freezes...it also shuts down when the H.H.D signal is bright red...

And when I switch on the computer, it always does the "Piiip" sound, but when it has lots of programs running, it makes a "Krrrr..." sound and then turns off with a "Pfff~rrreeeww...." sound, or something like that.