This happens to me more often than I'd like to admit, but i think it has to do with my cheap PC133 memory [and undue tweaking].
In your computer properties, there is an option "Startup and Recovery" in this there is and option about physical memory dump. turn this off, unless you are a programmer, or heavy sys admin. It is a dump of everything that was in your RAM to disk [X:\WINNT\MEMORY.DMP], so the file is wasting space [256 megs for me] on your drive.
-bZj