OK, you could try this little trick I often use especially when I have more than one instance of XAMPP on my PC - no need to uninstall your original version using this little trick.
Using the Control Panel, stop all the components, remove any ticks in all of the Svc boxes, if there are any and then Exit the Control Panel.
Rename your C:\xampp folder to C:\xampp_old
Now download the 1.7.4 Zip version and extract the xampp folder to your C:\ drive so once again you have C:\xampp - don't overwrite the xampp_old folder.
Run the setup_xampp.bat file to set your paths.
Download the new Control Panel from here:http://arloh.de/xampp/xampp_control3.0.2.zip
Extract the version 3 exe file to the C:\xampp folder and use it instead of the one contained in the release.
Now go to http://localhost
and after selecting your language see if all the demos work without issue - don't set your root password for MySQL and phpMyAdmin at this point.
Go to http://localhost/phpmyadmin
and make sure all is working as expected without using a password - close phpMyAdmin.
Next you can copy from C:\xampp_old your web site files.
Then go to the C:\xampp_old\mysql\data folder and copy and overwrite the contents to your C:\xampp equivalent folder which should now contain your databases and the system databases from your C:\xampp installation - nothing is lost.
(you do remember your root password though?)
Restart MySQL and then try and access phpMyAdmin using the root user/pass combo.
If problems at this stage then set your root password again from http://localhost/security/
Doing it this way you don't loose anything when reinstalling a wobbly corrupted XAMPP installation.
Good luck with this Jelle.