the computer is probably stuck doing something that is taking all its memory. it may be a corrupt file or it may just be too much unwanted stuff running in the background.
i can give you some advice on how to get rid of the stuff that might be causing it.
or if it is running well enough to do so i can log in remotely to clean it up for you.
if it just started happening recently you might want to try this first
System restore instructions - windows 7 or 8 8.1
hold the windows logo key down and hit Rtype rstrui.exe in the run box that comes up and hit enter
select restore to an earlier date.
Under the "suggested restore" which is usually not old enough to help is a link for "OTHER RESTORE POINTS"click that if the suggested ones are not BEFORE THE PROBLEM STARTED
choose a date that is BEFORE you experienced the problem
hit ok / restore
the computer will start to shut down
a restoring settngs box will appear with a status bar
when it finishes your computer will restart with the same settings it had on the date you restored to. your data will not be affected.
It is not perfect. But it fixes a lot of things.