I'm having a ton of problems with my HP 6700 printer since installing 10.10.4. My MBA sees the printer but shows it as sleeping. I can use the printer utility and connect to the printer, check the ink levels, etc. but the printer queue says the "printer is not connected" (yet, the utility sees it and connects to it). If I pause the printer in the queue and then turn the printer off and then back on, it then prints. It's driving me crazy...last night I had a bunch of docs to print and send to my accountant in a timely manner in order to get to FedEx before the pickup time and with each doc I had to turn the printer on and off. As you can imagine, I was one frustrated guy. It's seems to be going to sleep and not waking up when it's called. I'm using the Wi-Fi connection, not a hard wire.
I was able to print a doc from my iPhone so it seems to be some communication between the HP software and Window 10.