Nexus 7 flickering and won't charge

My nexus  7 hasn't been used/charged in a month. Today it wouldn't charge when I plug it in, it just flickers every 15 seconds. I opened it up and the connections with the battery were fine. help me!!

Might be that the battery charge fell below bla bla :-).  Try to leave it on charge for a little. 

P.s. opening it wasn't the best idea