JonB wrote:... The easiest thing to do is not make the XAMPP Apache (or MySQL if you have that previously installed as well) into a service...
Yes, I've found that even if you change to ports on the xampp instances, xampp will still load the pre-existing httpd if it's running as a service.
For the Apache you already have installed, if you are running Apache as a service, in Windows Service Manager, make its Start type - 'manual'. This way there won't be any start service contention.
If for some reason you need to run both, you would need to change the names of the prior-installed services so they are different than the default names that xampp also uses.
Apparently when the xampp Apache and MySQL are started, the program looks to see if if there is a matching service name and then starts it.