Today while working I got a blue screen of death. My Nvidia driver was giving me lot of grief for the past few days. the funny thing is that now when I try to log on I get the error message The group policy client service failed the logon. Access is Denied. I am 100% sure that I am entering the right password. If I reboot my machine couple of times then it sometimes it does allow me to login but it then says that c:\windows\system32\*** profile points to an invalid location and then I get an empty desktop which hangs again. How can I log in again? I will restore my OS back to a restore point before this whole nonsense of NVidia driver started Please help me this is urgent because my work has come to a standstill.

You seem to have a corrupt profile. You will need to log into the Built-In Admin account, remove your current account (make sure to back up your work before doing so) and re-create your account. Keep in mind, if your using the Built-In Administrator account as your primary account, you will need to Repair your installation. I figure it may be a combination of driver issues/spyware.

Also you may try System Restore in WinRE to back to previous versions.Arthur Xie - MSFT