A few years back I had problems like this when my computer wouldn't post on occasion. Turned out there wasn't enough power coming from the wall socket. Tested the plug-in with a voltage meter and was only getting 70-80 volts out of the 110 that it should have been... Replaced the plug-in with a new one and all was good... Bad house wiring was the culprit. Another thing to be wary of is brown outs, low voltage can be just as bad as surges in power.