Of the four iMac G3s that I bought, 2 of them do not work. The first broken one (A BB model) doesn't power on at all. The second one (Blue Berry) powers on but usually doesn't do anything beyond that (No startup noise, no logo on the screen, nothing.) I got it to work once, but after about 15 minutes, it gave me a "You need to restart!" crash message.

Obviously the first needs a new power supply, but I am not sure if the second one is facing a software or hardware issue. What does it need?

Thanks