90% of the time its something thats been installed recently.
Another game might have installed an older version of direct x.
Regardless.
Re install the game
Check Direct X for latest version
Check Video Card drivers for possible corruption, and re install.
Check for problem again.
Sounds like a connection issue to the game itself if you can log on etc..
If not, did you change any settings with your router recently?
Did you adjust your network layout by chance?
Re installing the game might solve it.
Im not sure why you would need to make a post without attempting these issues first, saving us all a lot of time with something thats not really TGC related. Take that hunch you have and attempt to rectify it with the possible solutions given to you above.