Bluetooth Speaker will not power on how can I fix?

I used the board out of and older Altec Lansing BT speaker and made my own box and used a bigger 50watt speaker and sounded great. Well I attempted to add a battery to my homemade set up and did something that caused the speaker to not power on. I connected the two 3.7rechargeable batteries in series and connected them to the speaker. I tried to turn it on and got nothing. I reconnected the batteries in parallel and got nothing still so I tried just one battery and still nothing. The board doesn't show any damage nothing seems to burnt so not sure what I did and would like to know if any one can tell me. What I might have done and if possible how can I fix it?? Thank you