OS 10.4 - Freezes on boot-up.Safemode doesn't work.

Hi. My iMac freezes on startup. I can't use safemode. The sleep light turns on. The fan and cd drive turn on as well. The screen stays black though. Once it got to the spinning icon that you see before the "OS is starting up" dialogue. Then it froze. I don't think my keyboard works either because the caps lock light doesn't come on. Everything else seems to work except the screen. When I had it on last it suddenly went unresponsive and a message pooped up that said something like. "Your computer needs to restart. hold down the power button to turn off." It had translations in 3 other languages (french, chinese, and spanish.I think).I couldn't do anything but do what it said. It froze the next time I turned it on. I can't turn it on in safemode. Thanks!