Boot problems; GPU fan at max

So, I pressed the power button to turn on the PC. One LED glowed, indicating the power supply(CX430) was turned on, but the power LED didn't turn on. Also, the GPU fan went to max. No beeps were heard from the motherboard speaker.
I turned the power supply off with its switch, and turned back on, and it booted, but stopped with a "CMOS Checksum Bad" message. I went to BIOS, set date/time and told it to load optimal defaults.
Now I'm typing from it.

What could have been the problem?
I haven't restarted the PC after that, so I cannot tell now if the problem persists, but I'll post back when I shut down the PC.

P.S. I would like to mention that when the power LED didn't turn on, there was nothing on the display either.