We need to rule out registry and hard disk corruption as the cause of this.
Do the following please
Download CC Cleaner (free) from hereCC Cleaner
(Click Download Latest Version on the top right)
Run it and let it scan and repair your registry.
Once done, restart the computer
Click Start, All Programs, Accessories, right click on Command Prompt and select Run As Administrator.
A black window will open.
Type in it
press enter and when it has completed, type in
It will give a message "the type of the file system is NTFS cannot lock current drive.
chkdsk cannot run because the volume is in use by another process. Would you like to schedule this volume to be checked the next time the system restarts y/n" Say Y, press enter and restart the computer.
Then tell me if it will now start please.