New
#2030
Mark Partition Active the Win7 100mb System Reserved boot partition (preferred if you have it) or Win7 partition.
Run Startup Repair - Run up to 3 Separate Times.
If it hasn't been too messed up then it should start Win7 and add XP to the Boot Menu. If not add XP using EasyBCD from Win7.
If Win7 won't start with SysReserved marked Active, move the Active flag to C to try repairs again.
If that fails, use Easy BCD from XP to transfer the System boot to Win7: Bootmgr - Move to C:\ with EasyBCD - Windows 7 Help Forums. But this may not rewrite the Repair My Computer link to F8 Advanced Boot Options, so if not run Startup Repair a few times until the link appears.