Is your PC sluggish and slow? Before you buy a new Computer:

Uninstall unwanted programs. It's easy, you can do it right now if you want, and it takes less than five minutes. For Windows systems, go to your Control Panel, click on Programs and Features. This will call up the list of programs your computer is running. Anything you aren't using?   Right click on each one and uninstall it. That's it. Once you're done, restart your system.

Clean up your Start Up folder.  It allows programs that you want to automatically start up when you start up your PC. Check the bottom right hand corner for applications that are running.  There is a little up arrow that will enlarge the list.  Some have a way to stop them from coming up at start up so that they wait until you request them to open.  (I also use msconfig from a DOS prompt, but that is getting a little more technical.)
And remember, just because you drag something to the trash can on your screen, doesn't mean you've deleted it. You need to empty out the recycle bin once in a while.
I frequently run a tool called CCleaner to free up space (the more space the better) and clean up.  Before messing with any of these things it's good to make a back up.  You should always have a backup, think in 3s too.  Your PC is one, then one backup can be nearby like an external hard drive, and one somewhere else.  I use 'cloud' storage called Mozy but the plan I have for Mozy is going away - my current plan is unlimited for home users....  The first backup protects against unexpected PC failure and the second offsite against a catastrophic disaster.  (Theft, Fire, Flooding and so on)  

The general rule is to back up anything that you would hate to lose and can't get back.  - Photos, Digital Movies, and so on.