I am getting white textures instead of proper ones, ie. white squares in place of a character, building, popups, sometimes whole backgrounds. Sometimes restarting the game helps, sometimes not, sometimes after restarting different things are affected. It's getting more and more frequent as I progress into the game. Anyone know a possible cause of this problem? Graphic card drivers up to date.

Core i5. Nvidia gtx 750. Windows 7.

EDIT: also sometimes I get transparent UI windows for buildings, ie. only buttons are visible and not the window itself, and sometimes the buttons are not clickable, the building behind the buttons opens instead or nothing happens.

EDIT2: Looks like restarting the game doesn't change anything, but things get fixed for a while after PC reboot. SOme memory problem I guess?