Verified install, then Uninstalled, Reinstalled, and it was previously working before the latest patch from impulse.

ATI 4850 is latest - Driver version 8.612.0.0 -  Picture below changes rapidly, flashing all types of strange shapes, happens on all maps.  Unplayable.

Reduced 62%

Original 958 x 540

What about the Catalyst drivers? Are yours at version 9.5?

Could your PC be overheating? Overheating can cause issues like large drop of frames and artifacts appearing on the screen, such as polygons and other weird shapes you have named.

Personally I have a Q9400 and HD4890 and they run Demigod without issues. They are very adequately cooled thanks to 6 case fans on my NZXT Tempest, but yeah, check if your cooling is sufficient.

IF the issues lies with overheating, then firstly:

1. Determine what temperature your card is running at first, and post it here if possible (regardless if its overheating or not, I've seen people claiming 100C being claimed as an 'OK temperature', when its clearly boiling water already)

2. Remove any overclocks etc.

3. Check if your HD4850's fan is spinning correctly.

4. Blow out any dust on the card by using some compressed air.

5. Use Catalyst Control Center and turn the fan speed up if it still doesn't improve.

6. Check your other hardware's temperature such as CPU using programs like SpeedFan or your BIOS and if they're also rather high (>70C or so), then your case itself lacks ventiliation.

7. If your case itself lacks ventiliation, then its a totally different issue.

8. If only your card is acting up, I suggest a RMA or purchasing a third-party GPU cooler. Not sure if there are any for a 4850, though.

For my HD4890, my idle temperatures run at 50-53C, and load hops to 67-70C. Thats pretty average for a GPU. For a CPU, mine runs at 35-40C idle and 55-60C under load.