Why do a lot of wierd computer problems happen? You can try my suggestion or ignore it, up to you. I've seen my share of bad Antec PSU's. I know they are good supplies but doesn't mean they never have problems. I'm just suggesting a method for troubleshooting.
You can also check the board's BIOS for power settings, try clearing the BIOS and redoing the setup in it. Other than these two things or a possible flaky motherboard, I would have to have the computer in my posession to figure out what is going on.