Make sure your Flash (as well as Shockwave, Quicktime, Realplayer, etc) are all up to date and that the most current versions are installed. Buwish is right about Flash being resource (CPU) intensive. Updating these viewer/player apps will help with that issue.
Also, make sure that you don't have unwanted apps running in the background without your knowledge, especially malware. I suggest you install, update, and scan with MalwareBytes (malwarebytes.org - the free version) just to verify you don't have any nasties floating about.