Some months back I swapped out my old Radeon 2400 Pro card that came with my Dell PC for a 6850.  The card has never worked as advertised due to driver problems.  Some games work fine, but Direct X is still autodetecting that I have a 2400 Pro.  No amount of driver installing seems to sort this.

Is there any way, short of a total system format of getting this card to work fine?

Did you try the new Catalyst Uninstall Utility and then installing the latest drivers?

Could you show me please where it's advertised as working on borked systems?

You really should reinstall that OS as it takes like 30 minutes. You probably spent much more time on trying to "solve" it in other manners.

CPU: AMD Phenom II X4 810 @ 3250MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 850/1100MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 95 x64 Edition, Lubuntu 13.04

CPU: Pentium 4 Northwood S478 @ 3200MHz | RAM: 1,5GB DDR 400| MoBo: Gigabyte GA-8S661FXMP-RZ | GPU: Abit Geforce Ti 4200 | Display: Dimarson 19" CRT | PSU: Noname 400W | OS: MS Windows XP Pro, Lubuntu 12.04

I might try that then.

To elaborate on my system.  It's an older Dell Inspiron 530 that has been upgraded.  Its a Quad Core Q6600 2.5ghz, 4gb of RAM, Windows Vista Home Premium with SP2.  BIOS is Phoenix AwardBIOS v6.00PG.  I can't remember my power supply but it was a higher rated Corsair PSU that I got when I got the new card.  I'm running DX11.

The old 2400 Pro was an actual card and not inbuilt, hence why I'm puzzled as to why Direct X is still saying I have a 2400.  Device Manager in Control panel says I have the 6800 series.  Some games when detecting graphics settings like Saints Row 3 will default to low settings but adjusting to higher settings works with no difficulty.  Games like BF3, or even older ones like Hydropobia Prophecy that autodetect and fix the settings aren't as cooperative.

Where can I get the latest version of the uninstaller.

Because windows has a wonderful thing called registry which breaks in 1 year even if you don't use the computer for anything else but reading websites. That's why it should be reinstalled at least once a year.

EDIT: I saw you posting it's not the OS then deleting it. I can prove you it is. Get a GParted live CD, make a spare partition on your HDD and install a second copy if the OS. Then install the Catalyst drivers. If it still reports the 2400 without ever seeing it, you'll get a Nobel prize.

CPU: AMD Phenom II X4 810 @ 3250MHz | RAM: Kingmax 2x2GB DDR2 800 @ 833MHz| MoBo: MSI K9A2 CF v1.0 (BIOS: 1.D)| GPU: Asus HD 6850 1024MB (DirectCu) @ 850/1100MHz | Display: L24FHD | PSU: PC Power & Cooling Silencer 750 Quad | OS: MS Windows 95 x64 Edition, Lubuntu 13.04

CPU: Pentium 4 Northwood S478 @ 3200MHz | RAM: 1,5GB DDR 400| MoBo: Gigabyte GA-8S661FXMP-RZ | GPU: Abit Geforce Ti 4200 | Display: Dimarson 19" CRT | PSU: Noname 400W | OS: MS Windows XP Pro, Lubuntu 12.04