[Need Help]Games lagging badly after upgrading to 7

did you install graphics drivers for you card, and what card do you have?

You will have to give us a little more info then that.

What graphics card are you using? How much space is on your Hard-drive?

After Installing did you update drivers?

I am guessing your motherboard lacks integrated graphics that means even updating graphic drivers wont do any difference.
If you are using old mobo like INTEL 945GC which is from yesterworld then throw it out and buy a decent Asus or Gigabyte G41 or G45 mobo that atleast has integrated INTEL HD graphics that would help you play DOTA 2
But don't expect too much untill you overclock your processor and buy a new graphic card

Im using Nvidia Geforce Gt 630 as my graphics card and there is still 129GB left in my hard drive and i did update my drivers after installing.