Sounds like you need to reinstall the Windows Boot Manager which may or may not work if you select automatic startup repair. You do not need any specific partition to be active for this to work, actually I think that doesn't really matter anyway. You can use a Win 7 Recovery Disc to fix an XP machine.
So to start off make sure you're using
these Win 7 recovery disc (so we're on the same page). Then follow these instructions:
1) Burn the ISO to a CD and boot from it.
2) Whether or not it detects your Win 7 installation, start the Command Prompt.
3) Type "diskpart". Then "select disk 0". Then "list volume".
4) Find your CD/DVD Drive in the list and note the letter that it has been assigned.
5) Type "exit" then "D:" where the letter "D" is the drive letter of your CD/DVD Drive.
6) Type "cd \boot" then "bootsect /nt60 SYS /mbr".
7) It should display that a new MBR has been written. Your Win 7 installation should now be bootable. I've use this method countless time and it hasn't failed me yet.