When you upgraded to Win7 was your previous OS on the same drive as Win7? Were you running a dual boot system with Win7 and WinXP or Vista?
Have you tried using the "bootsect /nt60 all /force" command from the Windows Repair Console? There is a write up about how to use this command here http://technet.microsoft.com/en-us/library/cc749177(WS.10).aspx
This command should reset your system to use the bootmgr for Win7 instead of looking for the ntlrd used by WinXP.http://technet.microsoft.com/en-us/library/cc709667(WS.10).aspx
also has a BCD rebuild command that you may have to try.