Hi
Delete all unnecessary trash off your computer (cookies, logs, histories, temps), make sure you have enough hard-drive space and then get into
My Computer>Properties>Advanced>Performance>Settings>Advanced>Virtual Memory>Change.
First check how much you have allocated to the main harddrive. Under "Custom Size" -- Initial Page File size is to be your total RAM number in Megabytes. Maximum size is however much you want and the lower your RAM the more you need. 1000MB on top of the initial size is enough if you have that much space and especially needed if you video edit and game. Press "Set" after you've set those values and OK.
That should be well now, but if it isn't be sure to report your total RAM and HDD space back.