I have had this problem in the past, and it almost always was a bad driver problem.
However, it could be a memory issue, so I would suggest that you have at *least*15% disk space available at all times, NOT including your swap file (paging file). For example, let's say you have a 100 GB hard drive, and your swap file (paging file) is 2 GB. 15% of 100 GB is 15GB, so you should allow for at least 17 GB free space at all times.
If your disk space becomes too limited and you don't have a crapload of ram, then the paging file (your virtual memory) can get constricted.
Another thing you should do as a matter of course is set your minimum and maximum page file sizes to the same value.
What would really help is if you took a look at your Task Manage/Performance tab, and report the values listed on that tab. That could give us a good idea of what's going on in your system.
Hope this helps.