Hi fraka (there is ALWAYS time for a short salutation, especially if you are asking for help on a volunteer community board and expecting polite replies on your request),
Please try to start the control panel with full administrator rights (rightclick on the control panel icon -> run as administrator). That try to start mysql there.
If this will be successful, you probably have a local user permission issue or Windows 7 UAC issue.
It would be very helpful too to see what is in your \xampp\mysql\data\mysql_error.log.
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