Theres a few things id try first:
- Check your firewall/AV - sometimes a patch changes the exe in a way that the FW/AV dont recognise it any more and you need to reallow AH.
- if the above didnt help, try turning Firewall and AntiVirus completely off
- check your VIDEO SETTINGS on first login screen, make sure they didnt get changed
- defrag the HDD the game is on (I dont really think that is really the cause. but it certainly cant hurt)
A note for reinstall: back up your Settings, Skins and Ahiiterr folders. Also Sounds/Sights if you use custom ones and dont forget films and screenshots.
After uninstall, you need to remove the HTC folder manually, as the uninstall wizard will keep the settings. Then reinstall from scratch. Launch game with default to see if that works... if yes, copy your custom stuff back in.
Hope this helps