Pull the battery out and test it. If it is defective and won't take a charge go to the Shark website and buy anew one by model number off the old batter. You can also try eBay using the number off the old battery pack.
Guys, I just realised that there is a mark called AC on the back of the module next to a gold small circle pad. Once you change the battery, you need to connect a wire or paperclip or something similar between the back or positive of the battery and the pad, it should then come alive. Good luck