I already try to searching this problem anywhere but it seem I don't find any solution, Guru please help this is my problem, when I try to start my computer it was only GUEST user account appear on logon and suddenly all my data and files is also gone from the desktop I don't know what cause it but I'm sure that because I login with Guest user account when I try to login to my Admin user account it was already gone, the question is how I can recover my account "admin" type and restore everything like before because when i try to restore system i can not the writte says "you don't have sufficient security privilages...bla..bla and so on because i can not use admin user account type what i try,
I already try to make NEW Admin user account in safe mode but when i enter safe mode there is no user account even exist on the logon the only "CLICKABLE"choice is turn off your computer HA! it seems i can not do anything to my computer and maybe the last worst choice is to reinstall it but maybe you can help me i'm not an expert to computer but i may be understand what should i do please help me whatever solution is appreciated.

oh yeah  :)I forget to writte my OS:
OS : Microsoft windows xp profesional
Service pack : 3
Version : 2002
224 MB RAM
I hope the last thing I do is not REINSTALL IT When you start your computer at the login screen press Ctrl+Alt+Del
Enter your username as administrator and leave the password BLANK.

Now create a new user account.

Use this guide to MIGRATE your old, corrupted account to the new one.
http://support.microsoft.com/kb/811151/wow!! that's great i think this will help i'll try it thank you so much for your help i'm very appreciate it mmmm...SORRY but it won't work when I press Ctrl+Alt+Del in the logon and entert administrator i leave the pasword blank and press ok but the words pop up it says "Your account has been disabled. Please see your administrator." wew how could this be??? Just checking, you've done what's suggested in this link --> http://windowsxp.mvps.org/admins.htm?

Also you may want to try system restore to restore computer back to a date you are sure the problem did not exist (if any system restore points do exist) --> follow the guide here if you nee help ....  http://support.microsoft.com/kb/306084Thanks for your advice but later after I try it again IT WORKS!!! yeah thanks for the help this is how it works;

1.Restart computer,
2.Press F8 quickly to go to safe mode,
3.Press Ctrl+Alt+Del in the logon screen,
4.Insert Administrator and leave the password blank,
5.Create new Admin user account thats it!!
you are now can logon as computer administrator 

but the last problem is I LOST ALL MY FILES AND DATAs 
but thanks anyway the important thing is I GOT my ADMIN USER ACC back! but if GURU have any solution Im very appreciate any help comes from The True IT my problem now is to recover all my files that lost!?

anyway but thanks to JJ 3000 you are very helping Create a new account and folow the steps from this guide:

http://support.microsoft.com/kb/811151/