I just ran into this problem with a clients computer. Ended up being a virus that sucked up all the space on the hard drive. What virus/malware protection do you have on your computer? I recommend downloading Avast! for virus protection and run a boot time scan, download and install Spybot Search and destroy and Malwarebytes. You can get all of these items from download.com. I would boot your computer into safe mode first. Press F8 when you computer first turns on and choose Safemode with Networking. From there, you should be able to get into the computer, delete a few files to install WINDIRSTAT. That will tell you where the virus(if that is what it is) is creating this huge file(or files) so you can delete them and install the programs mentioned.
Good luck
-T