I have a Gigabyte H55M-UD2H motherboard and an Acer S271HL monitor. When I connect the monitor to the motherboard via VGA, signal works perfectly. When I connect the monitor via HDMI, the system "sees" the connection, but the monitor receives no signal (the monitor shows a blue box which reads "No Signal" and then the monitor goes into power-saving state). Some fun facts about this: if I hook a different monitor to this box via HDMI, the monitor receives the output without issue (same computer/motherboard, same cable, different monitor) if I connect a different computer to the monitor via HDMI, the monitor receives the output without issue (different computer, same cable, same monitor) no signal is received whether in the OS or in the BIOS there are no BIOS options for controlling video output other than for selection of onboard vs. PCI/PCI-E-based video card (the system has no dedicated video card installed) The box is running Linux, so I have the output of xrandr which shows the connection and the monitor modes detected via DDC: ~$ xrandr --prop Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192 VGA1 disconnected (normal left inverted right x axis y axis) HDMI1 disconnected (normal left inverted right x axis y axis) Broadcast RGB: Full supported: Full Limited 16:2 audio: auto supported: force-dvi off auto on DP1 disconnected (normal left inverted right x axis y axis) Broadcast RGB: Full supported: Full Limited 16:2 audio: auto supported: force-dvi off auto on HDMI2 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 598mm x 336mm EDID: 00ffffffffffff000472ca028d128022 1c160103803c2278ca7b45a4554aa227 0b5054bfef80714f8140818081c08100 9500b300d1c0023a801871382d40582c 450056502100001e000000fd00384c1f 5311000a202020202020000000fc0053 323731484c0a202020202020000000ff 004c55573044303130383531300a01e5 020324f14f0102030405060790111213 1415161f230907078301000067030c00 1000382d023a801871382d40582c4500 56502100001f011d8018711c1620582c 250056502100009f011d007251d01e20 6e28550056502100001e8c0ad08a20e0 2d10103e960056502100001800000000 000000000000000000000000000000de Broadcast RGB: Full supported: Full Limited 16:2 audio: auto supported: force-dvi off auto on 1920x1080 60.0*+ 50.0 25.0 30.0 1680x1050 59.9 1680x945 60.0 1400x1050 74.9 59.9 1600x900 60.0 1280x1024 75.0 60.0 1440x900 75.0 59.9 1280x960 60.0 1366x768 60.0 1360x768 60.0 1280x800 74.9 59.9 1152x864 75.0 1280x768 74.9 60.0 1280x720 50.0 60.0 1440x576 25.0 1024x768 75.1 70.1 60.0 1440x480 30.0 1024x576 60.0 832x624 74.6 800x600 72.2 75.0 60.3 56.2 720x576 50.0 848x480 60.0 720x480 59.9 640x480 72.8 75.0 66.7 60.0 59.9 720x400 70.1 HDMI3 disconnected (normal left inverted right x axis y axis) Broadcast RGB: Full supported: Full Limited 16:2 audio: auto supported: force-dvi off auto on DP2 disconnected (normal left inverted right x axis y axis) Broadcast RGB: Full supported: Full Limited 16:2 audio: auto supported: force-dvi off auto on DP3 disconnected (normal left inverted right x axis y axis) Broadcast RGB: Full supported: Full Limited 16:2 audio: auto supported: force-dvi off auto on How do I get this monitor to recognize the output from this HDMI socket?