Antivirus don't stay the same.
They update their signatures in the background, and some may also update their behavioral blocking rules in order to block new virus threats.
You might try adding the game to your antivirus's exceptions list.
It won't hurt and might help.
If your computer's video card is only borderline at meeting the system requirements, you may have reached a part of the game which is more demanding. Check the menu to see if there are any graphics effects you can turn down.
Do you have the latest version of the game? There have been some updates to the original version, so if you don't have the latest version a patch might help. Which patch you use would depend on where you bought the game. You may have to get saves for the new version if you use one of the updates according to http://forum.daedalic.de/viewtopic.php?f=106&t=4518