really odd boot problem

Howdy guys,

This is the problem I have. When I turn on my pc it goes to windows is loading then after that just blackness, no hdd activity or anything. I hit the reset, tell windows to load normally and all is well.
This also does not happen everytime I boot the computer but only occansionally.

My machine is xp pro, 2 120gb drives, sony dvdrw, athlon xp 1800, 512mb pc2100 ram(though windows reads it at 480mb), audigy sound card, onboard video 32mb ati based. motherboard is at31 fusion.

I’ve haven’t seen anything like this on all the web. please help.

By the way why does my ram only read at 480mb and not 512mb in win?