You need to reinstall the Vista bootloader. Vista and 7 use a different bootloader from XP, which is why it doesn't work. It's also why when setting up dual boots, you install the older OS FIRST.
Spend some quality time with your search engine of choice to find instructions on installing the Vista/7 bootloader again.
Hi there can anybody help me please i have installed windows xp pro on a fijitsu siemens laptop which already had vista home basic on it i did not format any drives but wanted to be able to dual boot! however now i can only access windows xp and i rrealy need to be able to access vista as there are files on it i need ,i know i should have backed em up but u guessed i did not .Can anyone help me please .