If your GTA 4 suddenly stopped working (crashes after logging in to social club) here's a posible fix.
Try to open windows live market place and it should fail also.
Download windows live essentials
http://explore.live.com/windows-live...tials?os=other
Install any programm you want.
After the installation your PC will ask to reboot and do so.
Check to see if you can open the market place. If you can now login, then GTA 4 should also work properly .
It worked for me, I hope it will for you guy's too.