power

I have a P4 1.5 30gb 256mb PC here running win me.
I have major problems starting the machine. it tells me a different error message every time i start but the main one in Windows protction error. I found out that when I take the power cable out and put back in, it normally works. i have changed cable to no avail. It also reboots by itself sometimes when i do get in.
Please help.