Something similar happened to me with a canon printer I had. First it was one color then the other. It always happened after I put a new cartridge in. They said the jets were clogged or something and that it would cost almost as much to fix it as getting a new printer, so we got a new HP. The reason it happens, I think they said, is that you have to turn your printer on and off frequently (like daily) and we tended to leave ours on. When you turn it back on it automatically cleans out those heads, so it doesn't have time to harden and clog. At least that's how I understood it. Actually I have a ton of ink for a canon if anyone is interested...
