You don't need to go back to XP, you can directly install 7, and i'm guessing you have a new pc/laptop even if you go back to XP i bet there are no Drivers for your pc/laptop regarding to XP, so it won't work, i suggest backup all your stuff on dvds ot an external HDD in case you have a ton of stuff, now, if the error is about the videocard, uninstall the videocard's drivers and install the new ones from the NVIDIA official page, if you still have problems could be that the videocard is a bit loose giving you that error conflict, skype me my boy.