So you have not yet set a password and you have not copied over your own database yet?
This is the fresh ZIP install with no changes except the config to cookie?
Can you check with Task Manager that there is no other mysqld.exe running after stopping your current MySQL server from the XCP.
Apart from the MySQL in xampp_old you don't have any other MySQL installations on your PC and you removed any my.ini other than the one in XAMPP?
When you have stopped everything in the XCP click on the XAMPP-Shell button:
At the prompt type
sc delete mysql
click enter
If there is nothing to do it will say so.
Just trying to eliminate any sticking services in the registry.
See how this all goes.
Also won't hurt at this stage to reboot just in case there are issues with your last reboot then try again to access phpMyAdmin.