hard drive filling up by itself

My hard drive all of a sudden has decided to show its self as full and
filling more every minute. I have a new 3 month old HP laptop with a 140 GB
drive. I don't have anything that is taking up any amount of space and have
done everything possible to free up more space. I have deleted the old system
restore and shadow files , cleaned up the drive and deleted cookies and temp
files along with every unused program i had there is almost nothing in the
drive except what came in it and about a dozen or so very small programs i
had installed. In a matter of 1 hour today I lost 5GB of space by doing
absolutely nothing. Just a few days ago it was at 45% free. I had managed to
get it back to 47GB free but now it is back to 41 already and losing ground
fast. no unusual processes or programs running. nothing recently installed.
NEED HELP FAST