The first thing to try is booting into safe mode.
Do this by repeatedly tapping the F8 key as the computer is starting up, and choosing safe mode in the menu that is shown.
In safe mode, the administrator account (which is disabled by default) should pop up.
The built-in Administrator account is disabled by default in Vista. However, if no other administrative accounts exist on the system it may be enabled.
The password for this will be blank, and will allow you to login.
Once you have logged into the built-in Administrator account, go to Control Panel>User Accounts and create:
a. An administrative user account - call it "Admin" or the like. This account will only be used for emergencies.
b. A Standard user account or administrative account for your daily work. This will replace the corrupted profile. Remember, it is safer to work in a standard user account and use the Admin account when an elevation prompt asks for more permissions (like installing programs)
Set passwords as desired. Remember them or write them down and keep them somewhere safe. Especially for the Admin account, as you will only use it if something like this happens again!
Then log out of the built-in Administrator account and into your new user account so the profile folders/files are created. Do nothing else here right now.
Finally, log out of your new user account and log into Admin. While in Admin, disable the built-in Administrator account for security purposes:
Start >Search box>type: cmd
When cmd appears in Results above, right-click it and choose "Run as administrator". Now you will get the command prompt. At the command prompt type:
net user administrator /active:no
Hit enter and exit the command prompt.
If your original user account was corrupted, then while still logged into Admin, copy the data from your old corrupted user account to your new user account. OK any prompts you receive while navigating the other users directories.
Log out of Admin and into your new user account. After you are sure all your stuff is there, you can delete the corrupted user account from the User Accounts applet in Control Panel.
Let me know if this helps or if you run into any trouble,