Not really sure as to why but I'm noticing it more and more with electrical equipment these days, not just PC's. I've found that if something has stopped working, if I pull the plug, count to ten plug it in again and start it up, more often than not it cures the problem. First discovered it on a CCTV system at work. The company had a firm around to fix a failed camera, said it couldn't be done and would cost £100 + and was invoiced for a call out charge as well. I took a look at it, unplugged everything, put it all back and off it went!
Even applied the same principal to our fan heater at home.
It's one of the first things I do now when something seems to be dead.
What a strange and wonderful world we live in!