Do you have any form of setup diagnostics that came with your mobo? Maybe a system of 4 lights? If so look up in the manual what those four lights mean.
I had a similar problem and it turned out to be a dodgy memory stick - i would recommend trying another memory stick if possible.
AMD 2500+, 512mb Mem, 160GB (2xSATA 80GB in RAID0 array), K7N2G-ILSR (using on-board graphics and sound (for the moment ;-) ))
How many windows \"errors\" can there be??!!!