Vista wont load past welcome screen?

basically;
I restarted my laptop as it was going slow then it wouldn't log back onto my user.
I don't have the vista INSTALL disc as it didn't come with my laptop :S
I do have the repair disk for it though which i downloaded and have used before.

I've ran the 'start up repair' a few times and ran the memory thing.
cant system restore as had it turned off..
Not sure what to do.
Have tried running in safe mode also and i clicked on the spare user account and 'explorer.exe' would just crash and it would restart the computer.

thanks