Hlf-Life Exe error after Patch



After installing Half-life and completing the game I installed the patch for TFC. I then tried to run this and an error message appears saying my HL.exe is corrupted!! I have spoke to Sierra and they said to run an anti virus prog and reinstall. Did this didnt work. FDisked pc and tried again and this did not work. The error only occurs after the patch is installed does anybody have any ideas as this is getting very frustrating!!!