billpa, welcome to the forum! You're in the same boat that I'm in, I have the HP MS214 all-in-one, one model newer than yours. Our processor (CPU) is the same. What I did to improve performance was doubled my RAM from 2GB to 4GB, that helped a lot.
Other than upgrading your RAM & HDD, I can't tell you what else to do, hardware wise. However, mine was never as slow as you're describing, even running 2GB RAM, and Avast (at that time).
If you install and uninstall a lot of programs, you may have a lot of broken shortcuts, and all kinds of junk on your drive. Try using CCleaner, it can be found at:
http://www.filehippo.com/
While you're there, download & install "Auslogics Disc Defrag" (type it into File Hippo's search bar). Defragging will help a lot too. When using CCleaner, just run one sweep, as multiple sweeps wears out your HDD over time. But one sweep once a week will get rid of a lot of garbage. Run this before defragging with Auslogics.
But whatever you do, stay away from those programs that claims to be "all in one" solutions to "purge" your system of junk, many of these programs does more harm than good.
If you need further assistance, come back, we'll do our best to help.
Best of Luck,
Cat