It is VERY important to create a backup when you start modding GTA SA. Not everything looks great like we expected it to be.
I would make sure that I deleted everything gta SA related (except user files) and do a clean install again. As far as I know, I never get any conflict with antivirus - GTA SA.
Well anyways, do as Ezno said, and I'm sure you'll be fine.
Good luck, nub! <3