Cannot associate MP4-file to Windows Mediaplayer 9.0_Winxp anymore

Still on old Winxp-PC i wanted to associate MP4-file with Windows Mediaplayer 9.0 for winxp but failed.
Didnt know that wm.exe is hidden and wrongly associated setup-wem.exe. how can i get rid of it in the associating-programs-list?
Maybe this must be done before finding the hidden wm.exe.
I never had the problem before. yes i know the tricks how to associate when its not working in the first step.
maybe i must run/install lav-filters too.
Windows Mediaplayer is definitively not listed.
Maybe removing WMP and new installation. helped earlier. Thanks
For those following my neverending-problems-theme_
I am actually on a 500gb ide-hdd. the one which i wanted to backup but got two defective ide-drives.
nobody said backup must be done also on IDE-drive. Sata 500gb are still available and very cheap.
Firefox 48. Shockwave Adobe flash plugin not present so nothing to deactivate. Internet a bit slow. i will check that.

I should not wonder why: SP3 and final rollup 3.68 updatepack by winfuture not installed since was not able. Since i was finally successful in doing on two other drives i have great hope i can find the websites again.
i only know i must then start the files on desktop in admin-account. and the sp3 from winfuture maybe be corrupt.
when deleting update-log files i recognized i tried to install WMP11. maybe only working on SSE2-processor-PC which is not the case on GA-7N400 Pro2. Here i am fighting Capacitor plague. see other threads.

SP3 + final updatepack 3.68 installed inkl. most of the followed NFW-updates. more to come. WMP9 is running. seems version 11 not rrunning on this PC with non-sse2-processor.

Since i had to repairinstall earlier i had a Windows Mediaplayer Rollback from 11 to 9. It was clear i had to reinstall WMP 11 again. Since updates could be done i removed WMP 9, still listed as wrong 11. After installation WMP11 jumped back to the association-list. ET VOILA!
I am relieved since i am slowly setting up that old 500gb IDE-drive to normal speed. at least i hope. maybe i must clone to 2tb sata. first step was speeding up FB. i will report elsewhere since i have found hints in facebook-community..