Windows 7 Killed Vista

if you resized the partition that vista resides on, that's a very probable cause for your issues. otherwise i'd try running chkdisk and see what's up with the partition, it seems like you have some data corruption going on somwhere. if the MBR or whatever got fucked up by win7, you wouldn't even be able to get in. another possible thing is maybe win7 tainted the partition vista resides on somehow? but i rate that as unlikely.
tl;dr: run chkdisk on the vista partition