Computer came on with no display ... now works again, but why?

United States
November 8, 2006 4:08pm CST
I was working on an Acer desktop. The computer appeared to post and come on normally. There was hard disk activity. However, there was nothing on the display. I thought thast maybe the onboard video had burned out, so I was about to put a video card in the AGP slot to confirm my suspicions ... as I was pulling off a back cover plate, I accidentally dropped it against the motherboard. The computer came on by itself AND the video worked again!! I must have rebooted it at least 5 or 6 times since, both cold and warm boots, and it has continued to come on and work fine every time :) Anyone else ever run into the unexplained like this? Any hints as to what I can do to protect myself against this in the future?
No responses