C: Drive is full

My PC says my C drive is maxed out, but I'm positive I still have nearly 100 GB of breathing room. I've Googled it, ran scans, done everything under the sun, but I can't find where that 100 GB went. Finally, after using TreeSize Free, I see this "System Volume Information" folder hogging 98 GB. The problem? I can't open it and I can't delete it. What's the move here? (Running Win7 64-bit, by the way) Thanks in advance for any help

Did the System Restore get wiped? It usually eats up a ton of disk space if you haven't disabled it or dialed back the percentage used.

thanks, nice work!