My g4 cube is behaving very strangely lately. I bought it on ebay, and it seemed that every now and then, it would just randomly go to sleep or shut itself down. And now, it's started doing it so much that it's unusable. The power supply appears to be okay. I really think it's a software glitch or something telling it so go to sleep, and then restart or something. Once, it disconnected it's own modem before it "randomly" shut off. Any ideas?