Windows 7 Administrator account is missing on the login screen

I am trying to setup a VPN with windows 7 Pro machines without 3rd party software recently. The setup is not successful due to my very old vpn firewall router caot do PPTP forwarding. The machine I used as server to take incoming traffic makes me headache now. Its administrator account is just gone. I didn't realize this until today.

There are three accounts on that machine: HomeBook5Admin, user1, and myDaughter. Now only user1 and myDaughter account exit on the login screen. From the c:Users folder structure, I can see the HomeBook5Admin is there. I usually work under the HomeBook5Admin.

During the windows vpn setup, I do added two users for vpn login during the setup process but didn't added them machine wide. Now I tried to delete the incoming network setting but could not. Windows asks me the administrator password. I input my HomeBook5Admin password but the Yes button is still disabled.

Searched online for solution, someone tried Safe Mode. I used the Safe Mode but it surprised me because the Administrator account didn't require password there. And that Administrator account is not my HomeBook5Admin account.

I caot find anything useful I can do under the Safe Mode. I still caot find a way to bring back my HomeBook5Admin account there. There is no entry for my HomeBook5Admin under the Control Panel->User Accounts. I caot find HomeBook5Admin under the Computer management->Local Users and Groups as well. I check all the Groups, HomeBook5Admin is not listed under any of them.

And I tried to find the incoming network setting to delete it under the Safe Mode but it is not there because it is set under the HomeBook5Admin.

I am in my home network, a very old NetGear FVS318 VPN firewall router and then a Trendnet wireless router. I didn't configure any group/domain. They are in default, I think. we are using wireless almost all the time. But when this happened, that machine was coected with network cable.

So,

1. how can I bring back my HomeBook5Admin account? I have 32GB useful stuff with it including a virtual machine.
2. how can I avoid this happening in the future?