computer reboots itself every 10 secs

hi. just built my first computer this weekend and everything was working fine on saturday. on sunday evening my computer stopped working. somehow i fixed it but today the same damn problem occurs :

Whenever I start my computer , after 5-10 seconds it just dies and shuts down. Then 5-10 secs later it reboots by itself, works for 5-10 secs before dying again. Then it reboots itself 10 secs later.

I checked inside the Antec P182 once and saw that just before it dies, the computer tries to get the CPU-fan going....but it moves an inch and then stops - 1 or 2 seconds later the computer shuts down.

Could it be my Corsair 520W that is malfunctioning?

It just feels really bad to finally have a new system and then this happens
I'd really appreciate any help I can get in order to fix this as soon as possible.

I have not overclocked a bit.
also, how could the cmos become like this since the computers been functioning since this past saturday only??