If your power chair won't charge, it could be for a number of reasons. First, check to make sure that the outlet you're using is working properly and that the cord is plugged in securely. If everything looks fine there, the next step is to check the battery. Make sure that it's properly installed and that the terminals are clean. If the battery seems fine, then the problem may be with the charger itself. Try plugging it into a different outlet or testing it with a multimeter to see if it's getting power.
If you're still having trouble, then it's best to contact a power chair repair technician who can diagnose and fix the problem for you.