MSI K8T Neo2 troubleshooting

Hello

My computer won't boot up.

I just wanted to watch a movie, but the video was hanging up and getting stuck, so I thought the PC would need a rest. I shut it down for about 10 minutes.

After I started to boot it up again, It didnt get past the MSI boot up screen. Not even to the BIOS. It just stays on that screen.

I tryed taking the pc into parts and put it back together (which usually works in "fixing" the PC - also cleaned out the dust), but same screen after I put it together.

I assume it's hardware related, but maybe you can narrow down, what could be causing this.

Other details about the build that might be useful:

Radeon 9800Pro gfx
512MB RAM (UNB PC3200 written on it)
2 different HDD-s (shouldnt really matter which?)
Processor should be some ~2,2 GHz AMD I think.

I wonder if it could be that the little battery on the motherboard is just empty? I put this together around 5 years ago.