Are you using any new applications that are resource hogs like video editing?
Have you configured the computer to automatically mange the virtual memory?
The following instructions came from
this site.
# Click Start, then open the Control Panel.
# Click Performance and Maintenance, and then click System.
# Click the Advanced tab.
# Under Performance, click Settings.
# Click the Advanced tab.
# Under Virtual memory, click Change.
# Under Drive [Volume Label], click the drive that contains the paging file (virtual memory) settings that you want to change. In almost every case, this will be your C: drive.
# Click to select the "System managed size" option, then click Set.
# Click OK three times and restart your computer.