What is using up so much RAM? I can't see it?

Hey guys, I have a fresh install of Windows 7 64-bit that's around 12 hours old. After rendering a video with Sony Vegas my system became extremely sluggish so I checked the task manager and saw this: http://i.imgur.com/LD9cK.jpg

90-97% memory usage with no process claiming use of it. I am only uploading a video at the moment so nothing should be using that much. 8Gb of RAM currently installed.

I did allow Vegas more RAM before this happened (from 200MB to 2GB). I have reverted to 200MB and no change.

I will restart after this post and post back. If you need any more info just let me know.