I inherited a desktop computer from some relatives. It runs Vista great but occasionally, I can't power it up. I unplug the power supply for a few minutes, and then plug it back in. Try to power it up and sometimes the fan turns on and that's it. Then, freakishly, it will power up like normal. I do get the screen that says "windows didn't shut down properly" but i select to Start normally and its fine. Could this be the power supply? Do I just need a new power cord? Thank you.