Hi, Its a long shot but maybe it is on about the virtual memory. Loads of shortcuts to shortcuts on the desktop, loads of cookies and temp internet, no longer used programs where u havent deleted all the files all contribute to your lack of virtual memory.
Ive had it happen to me in the past until i cleaned up my comp. now i do a scan of all files once a month to check what rubbish ive collected.
Please ignore this if
a) u have done it already
b) this aint a problem.