Adminstrator A/c problem

Some strange things are happening with the built in Administrator Account.
There are other accounts on the machine with admin privileges which are ok.
Restricted accounts are also ok.

A summary of problems:-

The account is visible on the logon screen even though other administrator
privilege accounts exist.

Changes to the Desktop or Start Menu are not retained.

When trying to use Regedit there is the error message:-
"Registry editing has been disabled by your administrator."

Some start-up programs are not visible in the Taskbar even though they are
running.

Could it be that the HKCU registry hive that is loaded when the
Administrator Account logs on is corrupt, if so is there a way to copy the
hive from another account?

I thought about deleting the account and declaring it again, but I'm not
sure of the consequences. Any help would be welcome.

-----
Martyn