Computer Help.

I have an Emachines W3107. I added another hardrive of the same memory, and i doubled the RAM. and its worked great all along for about 4-5 months, but now, for some strange reason. Teh computer doesn't want to turn on.
When i press the power button, it starts up as usual. Once it shows me the E from e-machines (this is b4 it boots up the windows) and it freezes. Then i can hear the fans sloowly start to power down, until they stay at a low speed. The only way i can compare the sound is to a star wars movie.
Episode 4 when obi-one powers down the beam that holds down the ship. It sounds pretty much like that. i've also left it on to see if it heats up, and it doesn't.

If anyone has any idea what is it please tell me asap.

I've switched out the fans already.