Do i have work memory too short?

Hi, can someone help me please? I'm not a computer expert, i don't know a lot about these things. I"ve got a home computer about 2 years but now it's running slow. I haven't changed any setting or installed extra programs. All the programs i wanted to work with where installed by the shop dealer. I've put a new operating system on, changed from windows xp to windows 7. Any one can help out please?
