I've had a simmalar problem before like this, but i found that my computer would reset itself several times on its own before windows would load. With the problems i found and how you describe your problems i think we have had the same problem. I found the answer to be partly due to the graphics card (or driver). Replaceing this has cured the bulk of the problem (i still sometimes get the odd reset of windows before it loads but thats about it). Give that a try, you might want to check that your computer is clean inside aswell, dust can cause problems like this due to hardware getting too hot. Hope this helps
Simon, May 2006