PS3 fan not working ?

Ok i"m not sure if it's the "yellow light of death" because I can use it for a while.. For example I can get to a team deathmatch in black ops and get 2 or 3 kills and then bam! Everything freezes and thee PS3 turns off.... with the red light flashing. So after observing for a while I noticed the fan never kicks in like it used to, it complete silence... So if it's the fan, do you guys have any ideas? Please help :(