iMac G5, no picture, no chime light stays on

Got a problem with my iMac G5 15 inch. When I turn it on no chime plays, the screen is blank, and the light stays on. After about 30 seconds the fan kicked in at full blast with the computer doing the same stuff. Got it to work a while back after resetting the PRAM but now resetting it doesn't make a difference. Please help!!