I don't think it has to do with being fully charged. It could be that the hard drive cable is not properly connected. On a classic that I replaced the battery on, I ran into the same problem. I tried several different logic boards but still had the same issue. I went back to the original logic board and it started working. The point is sometimes you just have to mess around with it for enough time to get to work. It still could be a faulty logic board though. If you have the original logic board (and it is still working), try that one. Make sure to get it working BEFORE you put the case back.