What graphics driver do you have?
If you don't know how to see that, press start--> search "dxdiag". Then on dxdiag click on the display tab.
Search up that driver on google. On the list of results, only click on the one with your manufacturer of drivers' name. (For example if you have an Intel 555Blahblahblah driver, only click on the ones from the Intel website.)
Your driver will appear on the website. If it says "download driver", download it. If it doesnt, then search up that driver on the website, and it will turn out.
Most drivers haven't been upgraded into windows 7 drivers, but that's just fine. Even if it says "for windows XP", download it. REMEMBER WHERE YOU DOWNLOAD IT, because if you don't your dead.
Press Start--> Search "Device Manager", and open it up.
Click on the "display adapters" catagory.
Then Click on the "action" tab, and click on Add legacy hardware.
Click on "manually add..."
Then it shows all your devices. Click on display adapters, as that is your graphics chip.
You should see a list of drivers. Don't click on any of them. Click on "have disk"
It should open up your broswing directories (docs, C: drives, etc).
Find where you saved your download of driver.
Click on the graphics folder, then once you enter there you should see another folder, and an icon that looks like a piece of notepad with a gear on it. Click on that, then press ok, yada yada, it'll install. Your system will restart, and it should be better, lag and all.
If something's still wrong, than... oh well:)
USA pride. What now.