Well, the title says it all, i noticed that a friend of mine had similiar specs to my computer but he can run games at better quality and have higher FPS than mine. The one thing i did notice about his computer was that he has alot of hardisk space and he has very little programs installed in his computer. Does having alot of programs installed in the computer actually slow down or weaken your computer's performance?
Actually a lot of messy and unnecessary programs can slow down or even weaken you PC (malware adware or spyware programs can for sure). Another point is that not all programs uninstall completely after pressing uninstall button. Some of the files are left behind, and they can slow down you computer too. Advice is to launch "Uninstall Tool" program to check if there are such not-uninstalled-completely programs on your PC.
In general, not updated graphic card drivers can be the reason for lags in games.
having a full or almost full hard drive can cause your computer to act slower... however as far as the games running or not.... not likely.
as fred mentioned malware, virus, trojans, clogged up registry, etcetera can slow down a computer down. however just having programs installed isnt likely to affect you. the rest you want to take care of
as photon mentioned most likely your system is not the same as his or you are running on different settings. an overclocked gpu and newer (or more optimized) drivers can make decent difference. also running without shadows or aa or at a different resolution can be like night and day.