You could do a startup repair if you have the windows 7 disk
Boot fromm DVD - put the disk in and boot up Click: Repair your Computer (DO NOT CLICK INSTALL NOW) Choose windows 7 installation. Choose Startup Repair Click Finish
This should repair any corrupt files causing the problem. This may have to be repeated.
If this does not solve the problem try the System Restore option which you will find underneath startup Repair.
Once you are in business again do a complete virus scan. Can I suggest that you download free malwarebytes and do a scan using that.