auto detect analog error

I am trying to help my brother with his computer problem. He left it on overnight, and when he came to it in the moring he found it off. When he started it up, at first it would not come on. So then he unpluged it and then tried to start it again and as it started, he got the error on the screen "auto detect analog - going into powersaver mode, and then shut off. Then he could not start it up again until he unplugged it. I told him to try unplugging all cables except the keyboard, mouse and monitor. It still did it to him. Help, any suggestions.

That is a message from your monitor saying it couldn't find any signal to display so it is turning off.

It could be the CPU, the memory, the motherboard, or anything connected to it. Disconnect all the drives, pull any expansion cards, and leave only the keyboard and monitor plugged in and see if it will POST.