which answer do you expect from your request?
We don't have really much information about how you have installed XAMPP and which actions you have done since then.
"not working" is a really bad error report. Do you get any messages or entries in your log files?
You even haven't filled out your operating system field in your profile correct.
The only answer i can give you with that base of information is: By default the username is root and the password is not set, so it's empty.
If you have changed this, you should know to what value you have set the password.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~free software according to purpose of usageXAMPP 1.8
for local development/testing onlyZend Server 6 (free)
for production environments
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~It's like porn for programmers