Hey there, let's work through this frustrating second monitor black screen problem you're facing on your Dell M6800 post-Windows 10 upgrade. Since you've already ruled out driver updates and full system reinstalls, let's dive into targeted fixes tailored to this specific laptop model:

• Verify physical connections and display mode
  Swap out your display cable (HDMI, DisplayPort, or VGA) for a known-good one—faulty cables are a common culprit. Use the Win + P keyboard shortcut to cycle through display modes (Extended, Duplicate, Second screen only) and confirm Windows recognizes the secondary monitor in Settings > System > Display. Also, test the monitor with another device to rule out hardware issues with the screen itself.

• Tweak dual-graphics settings (critical for M6800)
  The Dell M6800 typically ships with a dual-graphics setup (integrated Intel GPU + discrete AMD FirePro M6100). Windows 10 upgrades can disrupt GPU-handling logic:

  1. Restart your laptop and enter BIOS (usually by pressing F2 during boot). Look for graphics-related options and try setting the GPU to Discrete Only instead of Auto-Switching.
  2. Open your discrete GPU's control panel (AMD Catalyst Control Center) and navigate to the display settings. Ensure the secondary monitor is enabled, and set a compatible resolution/refresh rate matching the monitor's specs.

• Disable Windows 10 Fast Startup
  Fast Startup can cause incomplete hardware initialization for external displays. To turn it off:

  1. Go to Control Panel > Power Options > Choose what the power buttons do
  2. Click Change settings that are currently unavailable
  3. Uncheck the box for Enable fast startup (recommended) and restart your laptop.

• Update BIOS and Dell-specific firmware
  Outdated BIOS versions often clash with Windows 10's display stack. Head to Dell's support page for the M6800, download the latest BIOS update for Windows 10, and install it (make sure your laptop is plugged into power during the update—never interrupt a BIOS flash!). You may also want to check for Dell's proprietary display-related patches for the M6800.

• Adjust power plan settings
  Some power-saving features can disable secondary displays unintentionally:

  1. Open Power Options > Change plan settings > Change advanced power settings
  2. Expand the Display section and ensure Turn off display after is set to a reasonable value for both battery and plugged-in modes. Also, disable Adaptive brightness if it's enabled, as this can cause unexpected display cuts.

Give these steps a shot in order—more often than not, one of these will get your secondary monitor working again. Feel free to follow up if you need clarification on any step!

内容的提问来源于stack exchange，提问作者drenovac