Have you run any of your system maintenance or scanned for any infections? A lot of people do not run regular maintenance on their computers. This should be done whenever you install or uninstall new/old software/hardware, to make sure everything is running alright. You should also run regular clean up of your drives and web files, as well as make sure you have the latest updates of what you are trying to run, like flash players, adobe, etc. Having a buildup of old log files/internet files can slow you down. A good product out there is call CCleaner. It's free, I use it rather than disc cleanup because it cleans up both internet explorer and firefox as well as your recycle bin and whatever else you set it up for all at the same time. Or you might need a system upgrade. I try to remove old install files that are no longer needed, you'd be surprised how many you can have. A few times I've just uninstalled everything completely (like adobe reader) then just downloaded the newest version getting rid of all those old updates.
If you are still having problems, and if you don't want to take your system into someone to have them look at it, your only option will be to try a reinstall.
My computer at work is so slow, but it is also 5+ years old. The hard drive is no where near full, heck it's not even half full. But with age things slow down, and I can't watch videos on it because it takes too long to load. Same with some sites, as more advancements come along, if a site has too many images or ads I avoid it and wait until I go home. I can't have more than a few tabs open at a time (along with my business program) or else I get virtual memory message coming up.
