just did a search for half life 2 ati fixes and seems there was a problem with catalyst once before and they bought out catalyst 4.12 drivers so im guessing its a catalyst driver issue in version 10.2 possibly
done that tinytomlogan still no joy even tried reinstalling directx but just looked on ati forums and found there are problems with all games running the u3 engine and also flight sims so i thinks its a case of just keep looking for new catalsyt updates till problem has been resolved other than that i can only think it may be a hard drive fault but cant see it to be honest.