Borked Vista 64 install

[starbuck]

Yesterday, my pc was fine. Now it will boot into windows but sit there for 15 minutes not doing anything(loads to desktop but doesn;t finish loading rest of startup progs and is unusable).

Safe mode keeps freezing as well.
Tried system restore and this doesn't fix the problem.

Think the only thing left is to reinstall vista.

Question is, if I try and install it over the top of my current install(ie run the normal install program and install it to the same drive as current install which should overwrite it) will it format the drive?

I have files on there I don't want to lose and I currently have no way of backing them up(I know should keep backups of important files to prevent probs like this).

I know you used to be able to install xp over an existing install while leaving normal files intact(photos, music etc). Can you do the same with vista?

[Agent]

When you boot off the disk, it should detect the install and offer to repair it - try that first.

The HD won't be formatted unless you tell it to do so