lol ghetto fan, ive so done that!
I hate random shutodown problems more than any other pc problem there is, because it could be anything. Usually it is overheating, to which you either gotta get a new fan or change your silicone heat sink on your cpu (this was what my wifes problem was in her case). it could even be a failing memory to a dying power supply.
I currently have this problem myself but only when i play games for about an hour, then it freezes and shuts off.
angers me because my pc is pretty clean and i have 4 fans running in there with no space for more, only difference is i have a new video card in there that ive never really pushed because im not a big PC platform gamer.
but generally your problem is certainly heat, so check your silicone and your fans! if you can get a program that reads your cpu temp and have it record it when it crashes so you can see if its persistantly the cpu.