@tim75247 since it "work fine when plugged into" but not with wireless I would start with a new battery. IF it still does not work, then you will need to tear it down further and check the circuitry. The battery should be in the Left side. You should have 4 screws under the ear cushion. 2 of those are regular Philips head screws and two are proprietary safety screws. You may need to try different screwdrivers for those (T5) to see if you can remove those.
If you are stuck with anything post a couple of pictures with your Question of where you are stuck at and hopefully we can assist you further, [guide|21499]