The reason that you may not be able to start MySQL is you have installed and uninstalled several times perhaps without making sure that all components were stopped and any services uninstalled first.
If you have port conflict issues then run xampp-portcheck.exe
and it will tell you what is using the ports.
Try this for the MySQL issue.
Run from the mysql folder mysql_uninstallservice.bat
Check in the control panel that the tick is no longer in the Svc box.
Now run from a command prompt:sc delete mysql
Next go to the mysql folder and run mysql_installservice.bat
Go to the control panel and check there is a tick in the Svc box and MySQL is showing that it is running - DO NOT click on the Admin... button or the world will come to an end.
Hopefully you can now access phpMyAdmin.