Problems with HP LaserJet 5100

If you were previously running 10.10.3 and have upgraded to 10.10.4, then try removing the LBP5100 from Printers & Scanners and then adding it again.

If you were using a previous version of OS X then try a reset of the printing system. This will remove all devices from Printers & Scanners but not the supporting drivers, so you will just need to add the printer or scanner again.

martí ferré wrote:

but the printer doesn't appear in the Add control panel

To see the printer in the Default view of the Add printer window, the printer must support the Bonjour protocol. There was a problem with Bonjour with 10.10.3 and earlier but this was fixed in 10.10.4. So assuming that the printer does support Bonjour then the other reason that can stop you from seeing the printer is that it is set to a different IP subnet to the Mac.

If you know the IP address the LJ5100 is using, then open a web browser and enter the IP address as the URL. This should result in you connecting to the internal web page of the printer. Does this happen? If it does work then it proves the Mac and printer are on the same IP subnet. If it doesn't work then check what IP address the printer is using.

Once you know the IP address of the LJ5100, then instead of using Bonjour to connect to the printer you can create a direct connection. To do this, open Printers & Scanners and click the plus button to add. In the new window, click the IP icon. Then enter the IP address of the LJ5100 and set the Protocol to HP Jetdirect-Socket. Leave the Queue blank and change the name to LaserJet 5100. Then select the LJ5100 driver in the Use menu and click Add to complete the setup. Now see if you can print.