If the new motherboard is similar or not too much different from the original, Windows 7 is a bit more forgiving than the old XP used to be, and will quite often boot up with no problem.
However if a major difference in motherboards and you do have a retail version of Windows 7 on disk, you should be able to use that disk to do a repair as stated earlier.

Last edited by Cornet Nev; 11/22/15 10:35 AM.