I'm so stupid! Now works fine, thanks furrywulfz! <3

My computer is really weak, but there are my specs:

Windows 7 64 bit Intel Core i5-3740 (3.20GHz 4 core) 16GB RAM NVIDIA GeForce GT 630

I have lags when game has a lot of effects. Someone can help me how I can fix it? Game generate strange "shadows". Look at this: