Can't login to XP

I am unable to login to XP. On the Windows "Welcome" screen, I see only the "owner" icon, which did not appear before, when login was automatic. When I click on the icon, it gives a flash and then returns to the same screen. I've booted in safe made and on the "Welcome" screen see two options, "administrator" and "owner." Neither one works, both giving the same flash and then a return to the "Welcome" screen. Your help is appreciated.

 

If you hit ctrl+Alt+Delelte twice at the welcome screen do you get the classic login? Try Administrator with no password if you do see the classic login. What happens?

 

When I hit ctrl+Alt+Delete at the welcome screen the first time, I am quickly shown the desktop wallpaper (no icons or start bar) before I can hit ctrl+Alt+Delete the second time. After a minute or so it goes to the login screen and the problem I initially reported occurs when I click on the login button.

Some additional info. I am running Win XP Home. It is an Dell OEM installation, so I do not have a disk.

 

Can't use the process to fix a corrupted registry, as suggested by TimW, because the very first step says: "Insert the Windows XP startup disk into the floppy disk drive, or insert the Windows XP CD-ROM into the CD-ROM drive, and then restart the computer" and I do not have a disk, as I noted above. Advice greatly appreciated!

 

How old is the Dell. I thought they came with an XP disc and a driver disc. Are you sure you don't have a disk somewhere?