And what was the reason to remove the battery?
What means you can't log on? You can't log on where? In your Windows? Or your PC is password protected through your BIOS /boottime password protection/ and you completely can't access it? Or it just crashes?
Just a suggestion:
Your BIOS settings are reset as a result of removing the battery. Usually it should autoconfigure itself right but I suppose for some reason it doesn't happen in your case. If you can access the BIOS check if something is wrong with the config.