Solve : Partition help.. PLEASE?!?

1.	Solve : Partition help.. PLEASE?!?
Answer» I have Windows Vista installed on my computer, but I made a new PARTITION so I could install Windows XP, because of how much faster it would be.. But now I can't change back to my Vista partition, I'm STUCK with the Windows XP one, which has problems on it. I NEED to change back to my Vista partition, but I don't know how. I tried changing the BOOT file (Start - Run - sysdm.cpl) but I've DONE something wrong, now my computer won't load any partition, I just get a black screen when I boot. I don't know where my Vista recovery disk is either. Any help will be appreciated GREATLY. EDIT: I get the option screen when I boot to select Windows XP or Windows Vista, but when I choose Windows Vista I get a black screen that doesn't change.. The Windows XP one works perfectly.

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