tw1x#GW

i have an older pc, but it's playable on low settings. however, when i leave structures instead of seeing the ground i just see through the map. i can see the tunnels on islands and walls flying. i've tried reinstalling the game, re-downloading it, and turned the settings all the way up (couldnt play like that, but was at least able to see if the ground was there and it wasn't) any ideas? running a pentium d 940, 4 gb ram, geforce 7950gtx