Causes
- Input source does not match the cable being used — the S2721DGF has two DisplayPort 1.4 inputs and two HDMI 2.0 inputs. If the active input in the OSD is, say, DP while your PC is connected to HDMI (or vice versa), the panel shows "No DP Signal" or "No HDMI Signal" even though the PC and monitor both work. This is the most common cause of the black screen on this model.
- Loose, bent, or damaged cable — the S2721DGF needs a solid link to carry 2560x1440 at 165Hz. A connector that is only partially seated, a kinked or worn cable, or a damaged DisplayPort latch drops the signal entirely and leaves the monitor reporting no input. The monitor has no built-in speakers, so there is no audio cue to help you notice the video link dropped.
- DisplayPort handshake failure on boot or wake-from-sleep — over DisplayPort, this panel is prone to a DP re-enumeration issue: after waking the PC from sleep, or on some boots, the screen stays black (or shows "No DP Signal") until the link is re-detected. HDMI is generally more forgiving on this model, and power-cycling the monitor or re-seating the cable re-establishes the handshake for many owners.
- Cable plugged into the motherboard instead of the graphics card — if your CPU has integrated graphics, plugging the DisplayPort/HDMI cable into the rear motherboard ports means the discrete GPU's signal is never sent to the monitor, an instant black screen on a gaming rig.
- A resolution or refresh the link cannot carry, or a PC-side boot failure — setting 2560x1440 at 165Hz over a marginal or low-quality cable (or the wrong port on an older GPU) can make the panel go black because the link cannot sustain the mode. A PC that fails to POST (loose RAM, cleared CMOS, or a crashed driver) sends no video, so the otherwise-fine monitor reports no signal.
How to Fix
- Power-cycle in the correct order — turn off and unplug both the monitor and the PC, wait about 30 seconds, plug both back in, and switch the monitor on first, then the PC. The S2721DGF's power LED is white when it has signal and orange/amber when it has lost it, so use it to confirm whether the monitor is actually receiving input while you work through the steps.
- Select the correct input source in the OSD — press the joystick/menu button and cycle the Input Source to the entry matching the cable you are using (DP1 / DP2 / HDMI1 / HDMI2). If your PC is on the DisplayPort but the monitor is set to HDMI, this immediately restores the picture.
- Reseat and check the cable, then swap the port — power down, remove the cable from both ends, inspect for bent or missing pins, and re-seat it fully so the DisplayPort latch clicks into place. Use a certified DisplayPort 1.4 or HDMI 2.0 cable and try the other DP/HDMI input on the monitor to rule out a damaged port.
- Plug into the graphics card, not the motherboard — connect the DisplayPort/HDMI cable to a rear port on your discrete GPU (not the motherboard video ports if you have a separate card), and confirm the GPU is seated and powered so it is actually outputting signal.
- Recover a black screen after wake-from-sleep — if the screen is black after the PC wakes, power-cycle the monitor (unplug 30s) or press Win+P on Windows twice to re-project and re-trigger the display handshake. Disable media-out/blanking at idle on the PC, or switch to an HDMI input, to avoid the recurring DP handshake drop on this panel.
- Lower the resolution or refresh temporarily — if the screen went black right after you enabled 165Hz, boot the PC (Safe Mode if needed), return the display to 60Hz at a lower resolution, reboot, then reapply 165Hz only with a good cable. If the panel still has no picture on any input, test it on another PC, laptop, or console to tell you whether the fault is the monitor or the computer.
- Check the PC if it is not posting — if the S2721DGF still reports no signal and the PC shows no other signs of life, reseat the RAM, and if you recently changed BIOS settings, clear the CMOS so the machine can boot and output video. If the monitor never displays on another working device either, the panel or board is faulty and it should be handled under warranty.