DVD Decoder Issues

Hi,

I am having a really annoying problem with my DVD drive of my Inspiron 6400 laptop.

I recently tried to play a DVD through all the media players on my system (Windows Media Player ,Realplayer and Media Center) and its come up with a similar message saying that I do not have the decoding software on my machine.

This seems strange as it never had a problem with playing DVD's before, seems bizarre that this decoding software should vanish from my computer? I know you can pay for software on line, but seems weird that I had it before for free  (can I get it back for free?)

The only thing I have done which I think that might have caused it was I recently removed media direct 3 through the add/remove programs option in control panel, is the decoding software part of this program, and my other media programs used this part of media direct.3? or is this just a stab in the dark.

I have tried to reinstall the program with the original disk (I have the original disks that came with the laptop, however the disk wont run through the installation as it says it already exists on my machine. So it doesnt show in my programs but shows when the installation disk is run. Any way to get around this (deinstall and reinstall correctly)

I have looked up this on the web and it appears that you may have to repartion drives and so on (sounds scary for a novice like me). But dont want to attempt this unless it will fix my problems with the other media players.

Any help or advice much appreciated.

Thanks

Steve