if you can boot then make a full backup and then restore from backup if it goes wrong, it is honestly not worth the risk. There are a couple of ways that you could get yourself into the position you are in, and without more detail, you'll be struggling. Explain precisely how you ended up where you are now, leave nothing out, and we might be able to help. I've been in similar positions and been sweating for many many hours to get it to work.