HP w2408h monitor isn't working with Windows 8.1???

I've been using my HP w2408h monitor as a second screen for my computer.  When I bought the new computer, I just connected the HDMI cable to the main monitor and it worked perfectly (with Windows 8.0 Pro).

Yesterday, I upgraded to Windows 8.1 Pro and the monitor no longer works / isn't recognized in the device manager.  I've tried to find drivers, but all I can find is drivers for 8.0.  I've read that the 8.0 drivers should still work for 8.1, but they don't.  I've tried reboots, reconnecting the HDMI cable, etc. - to no avail.  Can anyone help?