The answer is in the post i linked.
Of course you need to read it up to the end for sure.
Btw: Why did you have another Apache server runnig and still need XAMPP? Maybe it is an option to uninstall the other Apache server.
Changing the default ports can produce some issues. But that is also topic of the linked post you didn't read.
And for the port blocking Skype issue there is another Q&A
=>
[Q&A] solving Port 80 & 443 in use by Skype issue