Windows XP Logon Failure

[NickHigton]

I can boot up to the Windows XP Welcome screen (three users) without problem.
When I then try to log on as any of the three users, the system loads the appropriate wallpaper, but nothing else. After a short while it reverts to the Welcome screen and logs off. I then get back the Welcome screen with the three users.
I think I may have removed some files from start up using Symantec Systemworks.
Any suggestions on how to resolve this?

[patio]

I would try booting into safemode and using System Restore back to a point before you made the changes.

[NickHigton]

I tried this, but no luck. When I log in as Administrator, the original problem is still there - I can't get a personal profile to load from the Welcome screen.
I've also loaded Last Known Good Configuration a few times, without success. Does this take one step further back every time it is used?
I think the problem is that Windows itself is running properly, but cannot find any of my personal profiles.
I've also tried booting to DOS from the XP CD-ROM, but don't know enough to go any further with the commands available. I'd settle for being able to copy my data files to a memory stick, and then reformat the system. I do have the files backed up, but they are over a week old.

[patio]

Boot to the XP CD and hit R at the 2nd screen to enter the Recovery Console...At the Command prompt type in sfc /scannow and hit Enter.
This will repair/replace any damaged or missing System files.
When it has finished remove the CD and re-boot and hopefully the system will be back to normal.

[NickHigton]

Sorry, still no result. I got into the Recovery screen, which asked which Windows Installation would I like to log on to. I typed in 1, then pressed Enter when it asked for the Administrator password.
This got me to the C:\Windows> prompt, where I typed in sfc /scannow. The response was "The command is not recognised Type HELP for a list of supported commands".
HELP produced a list, that did not include sfc.
I changed to the c: directory, but couldn't get the command to work there either.
What else could I try, please?

[patio]

fixboot
fixmbr

Do them one at a time and re-boot each time.