insight into where these 11GB may have gone?
Hijacked by hackers? A rootkit and trojan infestation might have let your laptop join the zombie league.
Can you boot into SafeMode
using the F8 key?
Hard disk error? In Safe Mode, from the Start Menu choose RUN, type in CMD and press enter.
In the command line box type in: chkdsk /r /f then press enter (note the blank spaces before each /)
You can also try using the TreeSize free utility program: TreeSize Free 2.4