I would test out the occurence, but I am currently using Windows 7 (Microsoft just recently released the public beta on their site), which in structure is similar to Vista, but not a 100%.
Try safe mode first since there is no password.
Now also, were you provided a Recover CD, or do you have a partition witin the HardDrive to recover from. Mine for example included that originally, before I booted a new OS on it.
It may be possible to fix through Safe Mode, or save data that you need and recover it. However, also it is possible to keep all of your data when recovering.