Desktop Computer Won't Boot Up, Monitors are

Desktop Computer Won't Boot Up, Monitors are off, but Power light is on

Guys, this is what has happened.

(1) A few times, when I get home from work, my computer had unexpectedly turned itself off
(2) After pushing the ON button, the light turns on, but it doesn't BEEP and doesn't boot up
(3) The monitors are blank
(4) The fans are on

I've tried taking out all the components and wires and putting them back in, but nothing is doing the trick. The funny thing is that this has happened many times recently, but when I turn the computer on, it's fine. Now, this time, it just won't boot up, even though the power is on. My computer was behaving normally prior to this event.

I have an Acer AM5630-U5209A with upgraded 600mw power supply.

Thanks a lot for any help guys,
Josh