Did you set the root
user password in the XAMPP Security
page or from within PMA or where?
The PMA/MySQL password is easily set and changed using the XAMPP Security page mentioned above.
How did you uninstall XAMPP?
Make sure that all XAMPP components are stopped and any running as a service are also stopped/uninstalled including the XAMPP Control Panel.
Check using the Task Manager by right clicking on the Task Bar and selecting Task Manager then click on the Processes tab and look for any apache or mysql files - select and click on End Process if any are found.
Then delete the whole xampp folder.
Download a fresh copy of XAMPP and install again - test http://localhost
and all its menus first before proceeding.
Make sure in Vista you have administrator privileges for all things and you install XAMPP to a folder with no spaces in the name - c:\xampp is a good location.