Haus has given you a pretty good start.
Virtual memory is pagefile on your hard drive. When hardware memory becomes
full, Windows swaps data out of your installed memory to what once was
called the swapfile in Windows 9x and called the pagefile in NT, 2000 and
XP. This area on your hard drive is called virtual memory.
As Haus has suggested, first make sure your antivirus software is up to date
and run a scan of your system. Also make sure your system is clear of any
malware; download, install and run Ad Aware:
www.lavasoftusa.com.
If clear, go to Control Panel, open System, go to the Advanced tab, under
Performance, click "Settings," go to the Advanced tab, click Change under
Virtual Memory, select the option to let the "System Manage the size or
Virtual Memory, click the "Set" button, click apply and ok, reboot and see
if the problem goes away.