For now I would be disassembling the unit, redoing all internal connections, reassemble and try again. Whilst you've got it open, check the battery voltage but don't remove it. The battery retains some data, and perhaps a failed battery is the entire reason for your issues, but I doubt it. A very last thing to try would be new battery, and if that doesn't work then I think you need to be trying for a complete OS reload. Which you get an idea about here but is for a different model: