2001 2.2 over heating.

My wife has a 2001 cavalier 2.2 that just started over heating recently
I have checked all i konw to check and I am still stuck. The only problem i found is a leaking valve cover gasket, could this cause the problem? I don't really know that much about cars so any advice would be great

your valve cover gasket is not likely the problem. I would check to see if you termostat is sticking. You can check this by grabing the hose that come out of the top of the radiator if it is hot when the engine is at temp then the t-stat is ok. if it is not the your t-stat is stuck closed. if your t-stat is ok then i would look into the water pump.