There are many people who are facing an issue in getting their HP printers connected via USB to be detected on Mac OSX. If you are also facing the same issue, follow the steps below:

Disconnect all other USB devices
The Printer should be connected to the Mac directly, not through a USB hub
Click on the “Blue Apple” on the top left corner
Click on “About this Mac”
Now click on “More Info”
Under “Contents” on the left side of this window, click on “USB”
Verify that the Printer is listed under the USB device tree
If you still don’t see the printer, follow the steps below:

Unplug the USB cable, Shut down the printer and then shut down the computer. Wait for 2 minutes before restarting the Mac. This allows Mac to reset the USB addressing
Turn on the Mac, then turn on the Printer and reconnect the USB cable
Run the HP Setup Assistant again
If the problem still persists, launch the HP Setup Assistant and immediately follow the steps below:

Launch Process Viewer [Hard Drive--> Applications-->Utilities-->Process Viewer]
Locate HP Communications in the “Name” list and click on it to highlight it
From the process drop down menu, select “Quit Process”
Close the Process Viewer
In the hard drive, go to Library–>Printers–>HP. Launch HP Communications.app from here
On the HP All-in-one window, click on “Rescan USB”