Windows Vista Video Card Problem

>I use Windows Vista Ultimate SP1 which is Activated and completely
> functional.. not ever had any issues with Hardware / Software until one
> day I
> was just using Windows Media Center and went to play a Video and the
> playback
> was really slow.
>
> The Audio would play fine but the video would play in slow motion. This
> happen completely randomly without any reason. Anyway, I quit Media Center
> and there was a notice saying that my Graphics card does not meet the
> minimum
> requirements and that some features may not work correctly.. So I started
> Media Center again and noticed that none of the animations were working
> and
> when I tried watching TV it said that it was missing files required to
> work.
>
> Anyway, I played the Video using Windows Media Center.. same problem!
>
> My Graphics Adapter is: ATI ALL-IN-WONDER X800 PRO with 128 MB VRAM. So
> there should be NO problem at all with meeting minimum system requirements
> and has a Rating of 5.2 in the Windows Experience Index.
>
> I downloaded the Latest ATI Display Drivers after using the Windows
> release
> from Windows Update (WDDM) to see if it would make a difference... no
> change.. I removed the device from Device Manager and Re-installed from
> scratch removing all previous driver information.. Still nothing had
> changed.
>
> In the end.. I backed up my documents and Formatted the disk and
> re-installed Windows Vista and installed the SP1 update via download from
> Microsoft as the Full size Download instead of waiting for Windows Update.
> Everything seemed fine.. Media Center was working correctly, Video's were
> playing fine.. No problems at all!
>
> I started to re-install the software that I had before.. nothing major..
> just applications like Windows Live Messenger and iTunes etc..
>
> Then ran Windows Update and got all the available updates and shut down as
> normal.
>
> Then I start the computer again the next day and everything seemed fine,
> no
> problems displaying Windows and no lagging / slow performance. Started
> another update and finished it all.. shut down then logged back on a few
> hours later to see that everything had gone back to the way it was before
> I
> re-installed Vista with no video's playing properly.. and Media Center's
> Animations disabled and the warning message about the system requirements.
> So
> now I started to suspect it may of been an actual physical problem with
> the
> card.
>
> I have a spare hard disk that I installed Microsoft Windows XP Service
> Pack
> 2 onto and ran for a little while so I booted into XP and ran Microsoft
> Update to get it up to date! Left it for a few days working fine.. no
> problems..even games run smoothly!! So it seems to be an issue with
> Microsoft
> Windows Vista SP1! I need to be able to continue running Windows Vista
> because not just have I payed for it... I need the Media Center
> Functionality.
>
> Please help me to resolve this issue.. if more information is needed then
> I
> can provide it quickly!
>
> Thanks In Advance
>
> Aaron Roberts