iPad worked great. Went to sleep and never woke up.

My iPad worked great and had no issues. My iPad went to sleep and never woke up. When I needed to use my iPad again it wouldn't turn on. I plugged it in and it didn't register that it had been plugged in for charging. I took it to an apple store and they said it had "mid system failure". I just replaced the battery on it and it has the same issue. My next thought is to check the connector pins. I'm not positive on what "mid system failure" means, but I was curious if any one had any idea and what I should check next or should be checking instead? Any help is appreciated! Thanks!