Boot into the Recovery Console and run the CHKDSK from there, let it finish and see if you can get in then.
CHKDSK /R is what you want to type in at the command prompt.
The chkdsk service that is running may be autochk.exe.
Typing this may stop the chkdsk servcice
net stop autochk.exe
If that does not work try the article.
http://support.microsoft.com/default...b;en-us;307545
It basically puts in an older registry so you can boot the computer, and then take a regestry out of a recent restore point.
GOOD LUCK, let me know how it goes.