PC Query - Loads of Space used - why?

I have a 1TB hard drive and have just cleared some games and stuff of it to use as a work pc. Even with the game data gone there's still 156/7gb worth of used space showing up in the partition manager and I don't know why. Has anyone got any ideas what could be using all this space? I have no videos, games or other large files. The biggest programs I have on it are Sketchbook Pro and Openoffice, it's baffling. I'm guessing win7 takes up quite a bit, but surely not that much???

via JREF Forum http://ift.tt/UeP6s6