Mac Pro won't boot-loud fan noise

Hey everyone,

My Mac Pro suddenly does not boot up anymore. It has always worked perfectly.

I hear the fans starting up and the chime, but then nothing happens. The fan connected to the ATI Radeon just keeps going and going (very loudly). Nothing appears on the screen.

I'm not sure if this is a video card issue, the logic board....

Got your original install discs? Pop in disc one and run Apple Hardware Test which will check out logic board, video card etc.