04-18-2016 06:47 PM - edited 04-18-2016 07:03 PM
Based on the discussion in this forum, it seems to be a firmware issue.
On my system, it's ALWAYS repoducible and the 'workaround' ALWAYS worked.
ThinkPad: P50, i7-6700HQ, Intel HD 530, nVidia Quadro M1000M, 64GB RAM. BIOS version: 1.23.
Monitor: Dell P2411H
Laptop to Monitor connection: HDMI to DVI. (Also tried HDMI to HDMI, same result)
OS: Windows 10 Enterprise X64.
BIOS Display Mode: Hybrid
OS Desktop mode: Extend desktop to external monitor.
1) External monitor was working properly.
2) Shut down Windows.
3) Unplug monitor cable from laptop's HDMI port.
4) Start Windows.
5) Shut down Windows.
6) Reconnect monitor cable to laptop's HDMI port.
7) Start Windows.
8) External monitor is not recognized anymore. (like it never exists)
The above is a very common use case. Step 2, 3, 4 and 5 is what happens when I leave the office and go to the field. Step 6 and 7 is when I'm back to office and try to reconnect my external monitor.
1) Get into BIOS > Config > Display. Change from Hybrid to Discrete. Press F10 to save config and reboot. (if you're OK with 'Discrete' mode, you may skip step 2 below)
2) Get into BIOS > Config > Display. Change from Discrete to Hybrid. Press F10 to save config and reboot.
3) Monitor is recognized and everything is back to normal.