Could you please re-install GTA? Better than doing anything that will take alot. "But, don't install the same GTA that you've.
This may help you!
If nothing happens, know you had network stack problems once before and they might play a role here too, so please download
this: and run it as Administrator.
When it completes, restart your PC, and after that;
Please download, extract and run MTADiag and follow the instructions.
Press 'n' when asked.
EDIT: If there is nothing happens and CIT not worked fine. It's most likely it will be resolved after running the file (make sure, as per the instructions, to rightclick > Run as Administrator, let it finish on its own without closing it, and then reboot. It can take a while and may even appear to hang, which it's not). If that solved it, please let me know in here.