When I´ve been playing for a while my screen gets "messed up". All textfields display strange messages in different fontsizes!!??. Background graphics get distorted af corrupt to the point where you can hardly see whats going on and if I reeboot my computer it's OK for a while and the the same problem re-occurs. Any ideas. please...

(I´m running a 1.6GHz processor with nVidia GeForce 4 128MB Video Card).