From : hey whether u are having windows 7 later this problem is also ...

hey if u are having windows 7 then this question is also faced by me it is totally simple to do just google all for ''fixshell for windows 7'' and download the exe profile ''fixshell' put fixshell.exe in ur usb drive root from different computer or laptop lash out up ur pc keep on pressing f8 then a menu appears then select ''safe mode with command prompt'' when command prompt appears author ur USB ACTUATION message IM taking it X: put''X:fixshell.exe'' press enter next it will talk to all for reboot select yes and ur lapi will be fine

Source: http://answers.bumpkin.com/question/index?qid=20110318215556AAhtmqn