Errormessage and WMP failure after Windows update

Help I’m totally stuck.

After an automatic update a week ago an error message (MSP PNP Notification
window: Msmsgs.exe) pops up every time I start the computer saying that the
procedure start address ExtT in the DLL-file GDI32.dll can’t be found.

This has resulted in that the Windows Media player does not work. Every time
I doubleclick e.g. a mp3 file the same error message occurs.
Also my Nero burning software does not work.
I tried to reinstall Windows Media player but the same error message showed
up during installation.

Every time I close the computer it tries to install “Security update for
Windows XP (KB961373)� but seems not to succed with it either.

I run Windows XP Home Edition Version 5.1.2600 Service Pack 3 build 2600.

I tried to restore the system to a week before the latest updates and then
everything works fine without error messages, but as soon the Windows updates
are installed again the error reappears.

What should I do? What does ExtT do? I can’t find any info of this.