Why my pc run slow..........................…

You may have 4gb of ram, but you also have windows 7. What I mean is your computer isn't that amazing, and you shouldn't expect it to run max settings perfectly fine. All I can suggest is run a defrag, clear your cache. This may be too advanced but if it were me I would install 64 bit xp. Xp so it can run much faster, and 64 bit so it can recognize all 4 gigs of ram.