System 5 error hmm...? I'll look into it, even though I'm late...lol.
Edit: So anyways, a system 5 error is an authorization error as you may know. It's when you have someone has dual permissions, and you do not have the highest power (simplifying it). Even if you are able to create a second administrator account, then you would not be able to get back into your old one. It works similar to these forums, or any forums. The default administrator group (owner) has more rights and abilities than the secondary administrator group we created. One suggestion by microsoft was to reassign the permissions to your hard drive. I'm not exactly sure what you could do at this point...
I recently came back after being afk for a moment and it hit me. Just use cmdkey to find your password. All you need to do is type...
cmdkey /list:(target name)
If this can't help you, I'm sorry but I do not know what could. I might be able to research the topic a bit more. Perhaps ethan could help you if I could not.
p.s. I hope I'm not way too late to help with this and it has already been solved.