hiding administrator account

please help... the other day my sister opened two new accounts in our computer, one for her(admin) and one guest account, with the admin's(original), 3 altogether user account. i was installing new softwares using her account but when i re-boot the computer, the admin account disappeared. it was password protected and hers isn't. anyway, i restore the computer and was able to get the admin account back... and then i changed the admin's account to hers (name, password, etc.) and the new account to mine. and then it happened again. when i re-boot the system, the computer went to log-on directly to my account and hers(original) disappeared. only this time i can't use system restore anymore. i looked at computer management and hers(original) is still there... but i don't know what to do. please help... thank you.

 

Is the actual name of the admin account "Administrator"? If so, Windows might be hiding it on purpose for security reasons. Try creating an account with your name or a nickname and give yourself administrative rights. If you need to get back into this admin account to do that you can boot in Safe Mode (press F8 key before windows startup) and Administrator will show up then.