My power mac 2.3 recently start acting up.

Here is what is does:
1. The screen will go black.
2. The fans will steadily speed up to full speed in about 1 minute.
3. If I reboot it will work for a random amount of time.

I though it might be a heat issue so I cranked up the AC in the room and it didn't fix it.

The system worked fine since I bought it used earlier this year.

Any ideas?