also read this thread if game runs slowly. i have tried to make it easy for everyone to understand https://forums.uberent.com/threads/how-to-improve-frame-rates-all-video-cards-driver-links.53165/
try this.. http://steamcommunity.com/app/233250/discussions/2/810938810899540110/ if that fails, then yes upload dxdiag.txt again and PA log file
4GB is very limited RAM for PA, try to close all browsers and any other software before start PA. Also there still might be some memory leaks, so you might want try to restart PA when you finished to play one game. Actually your system shouldn't freeze just because of out of RAM, but most likely it's a bit worse on Vista.
