Even after many years of dealing with computers I am still amazed at the numbers of ways that users find to destroy them!
From the information you have given so far, assuming a typical installation, there were three accounts on this computer:
1) The Administrator account (RID=500)
2) The Guest account (RID=501) normally disabled and locked
2) The "user account" (whatever it was called) (RID=1000 or greater)
Do not be swayed by the "user account" still being displayed on the login screen. All that tells you is the name of the last person to login, nothing more. It does not change, even if the account is destroyed, because it is only showing a value copied from the registry.
I know you have said that password recovery is not the issue here, but the password utility I have in mind will establish what user accounts still exist. You will need access to another computer with a CD-RW drive, then access to the broken computer.
Download and burn to CD, Petter Nordahl-Hagen's chntpw from
his website. Read the instructions on his site thoroughly, then boot from the CD you have made. Follow the script that scrolls on-screen right through to editing users and passwords. At this point, a list will be shown, something like the following:
RID 0x1f4 Administrator
RID 0x1f5 Guest
RID 0x3e8 "user account"
You may see one, two, or all three of these depending upon what has been destroyed. It is not important to understand exactly what an RID is: just think of it as a user number. RID=500 (my top list) is the same as RID=0x1f4 (on-screen list) because 500 in base 10 = 0x1f4 in base-16 arithmetic.
By carefully following the on-screen prompts you can see this list and then exit without causing any damage. All you are doing is reading the disk. Depending on what you see, you could try logging in as the Administrator, or you could post your findings or further questions in this forum.