Currently I can login to windows 7 if I boot from CD rom and ignore the prompt to use the boot disk.
When you try to boot normally what error do you get ?
Boot from the CD
When you reboot you will see this although yours will say windows 7. Click repair my computer
http://i1224.photobucket.com/albums/ee362/Essexboy3/RepairVista_7275.jpg
Select your operating system
http://i1224.photobucket.com/albums/ee362/Essexboy3/RepairVista_7277202.jpg
Select Command prompt
http://i1224.photobucket.com/albums/ee362/Essexboy3/RepairVista_7277.jpg
At the command prompt type the following
Bootrec.exe /FixMbr
[*]Once finished type Exit
Reboot to normal windows and run MBRcheck again please