Ok, well I'm trying to figure out if this computer will support another monitor or not. I don't really care about quality, it is being used for MS word documents and an accounting program, it doesn't matter if it looks like crap.
Open ports specifications of your HP All-in-one PC and read whether the port you're trying to make the connection with supports video-out or not. Even, I tried to connect my Lenovo All-in-one PC with my Macbook so that I can use my PC as a secondary monitor for Macbook, but later I found that my PC monitor supports only video-out.