You aren't giving us very much to go on, such as system specs, recently installed apps, etc. If the games are running slow, check for background processes that are taking up resources, run some virus scans, and go through the usual clean-up and maintenaince procedures. Also, if this was a pre-built system, it probably shipped with a lot of junk on it that can be removed and clean up as well.
You could start by filling out your system specs section.