Hi mutski,
uninstalling is easy, just move or delete the JoyPad.dll file in the Plugins directory (C:\Mach3\Plugins\).
When JoyPad.m3p is installed, it is just renamed to JoyPad.dll and moved into the Mach3 Plugins directory.
If you still have problems after removing the JoyPad.dll file, it is not caused by the plugin.
Hope this helps.