You've got two Dell U2723QE monitors daisy chained over DisplayPort, the picture looks great on both screens, and then you plug a thumb drive into the side of the second monitor. Nothing. No drive letter, no chime, not even a flicker. The USB hub on that monitor is just sitting there dead.
This is one of the most common calls we get from folks who just upgraded to a multi-monitor setup. The good news is the fix is almost always the same, and it takes about five minutes. The bad news is that a lot of people chase the wrong problem for an hour first. Let's skip that part.
Cause 1: The USB upstream cable was never connected (or got moved)
This is the cause about 7 times out of 10. DisplayPort carries video and audio. It does not carry USB data between the monitors. The USB hub on a Dell monitor has its own separate upstream connection, and if that cable isn't plugged in correctly, the ports are dead. Full stop.
Here's the part that trips people up: on a daisy-chained setup, each monitor's USB hub needs its own data path back to the computer. The DisplayPort daisy chain only carries the video signal from Monitor A to Monitor B. It doesn't carry USB from Monitor B back through Monitor A to your PC.
What to check first
- Look at the back of the second monitor (the one downstream in the chain). Find the port labeled
USB UPorUSB-B UP. On a U2723QE it's the square USB-B port near the DisplayPort In. - If nothing's plugged in there, that's your problem. Run a USB-A to USB-B cable from that port to an open USB-A port on your PC.
- If something is plugged in, trace where the other end goes. I've seen people plug the USB-B end into the monitor's own downstream port by accident, which does nothing.
The USB-B upstream cable is a data cable. It's not optional. Dell ships one in the box for exactly this reason, and half the calls I take are from people who left it in the box.
What you should see after plugging it in
Within about 3 seconds of plugging the USB-B cable into your PC, Windows should make the device-connected chime. Open Device Manager (Win+X, then M). Under Universal Serial Bus controllers you should now see a generic hub entry, often labeled something like "Generic USB Hub" or with the Dell monitor name. Plug a flash drive into the monitor's side port. It should show up in File Explorer within a couple of seconds.
If it still doesn't work, try a different USB-A port on the PC. Front-panel ports on some older cases are flaky. Rear I/O ports on the motherboard are always the safer bet.
Cause 2: MST is off, so the second monitor isn't really part of the chain
DisplayPort Multi-Stream Transport (MST) is what lets one DisplayPort cable carry video for two or more monitors. If MST is disabled on the first monitor, the second monitor might still show a picture in some odd configurations, but the USB hub handoff never happens properly. This one is sneaky because the video looks fine.
How to turn MST on
- Press the joystick or menu button on the first monitor (the one directly connected to your PC).
- Go to Menu > Display > MST.
- Set it to On.
- Power cycle both monitors. Unplug the power from each for 10 seconds, then plug them back in.
After the power cycle, wait about 15 seconds. You should see both monitors come back with the same resolution and refresh rate you had before. Now check the USB ports on the second monitor again.
The DisplayPort version gotcha
On many Dell monitors you'll also see a setting called DisplayPort 1.2 or DP 1.4 in the same menu. MST requires DP 1.2 or higher. If it got flipped to 1.1 somehow (usually by a firmware reset or a factory default), MST won't work even when it's set to On. Set it to DP 1.4 unless you're on a very old GPU.
Also check your GPU. If you're on an older card like a GTX 960, MST support is spotty. The real fix in that case is to skip daisy chaining and run two separate cables. It's less elegant, but it works every time.
Cause 3: Insufficient power or a bad cable in the chain
Dell monitors with USB hubs need enough power headroom to run the hub. If you've got the monitor plugged into a power strip that's already loaded down, or if you're using a cheap third-party DisplayPort cable that doesn't meet spec, the hub can brown out and just stop responding. It'll still pass video because video uses less bandwidth and tolerates more slop.
What to try
- Plug each monitor directly into a wall outlet, not a power strip. Test again.
- Swap the DisplayPort cable between the two monitors for a known-good one. Dell ships a decent cable with U-series monitors; use that one if you still have it.
- If your monitors support USB-C upstream (U2723QE and similar do), try using USB-C instead of USB-B for the upstream data. It's a cleaner single-cable setup and it eliminates a whole class of cable problems.
- Check the monitor's firmware. Dell publishes updates on their support site under your specific model. Firmware bugs on early U2720Q units caused the USB hub to drop out after about 30 minutes of MST use. If you're on a U2720Q with firmware older than M2T104, update it.
After any of these changes, give the monitor a full power cycle. Not just off and on with the button. Unplug it from the wall for 10 seconds. The USB hub controller on Dell monitors keeps state, and a soft power off doesn't always reset it.
Quick-reference summary
| Cause | How to check | Fix |
|---|---|---|
| USB upstream cable not connected | Look at the USB-B UP port on the second monitor | Run USB-A to USB-B from that port to your PC |
| MST disabled | Monitor menu > Display > MST | Turn MST On, set DP version to 1.4, power cycle |
| Power or cable issue | Swap cables, try wall outlet directly | Use Dell-supplied DP cable, update firmware, use USB-C upstream |
Start at the top and work down. The USB-B cable gets you fixed most of the time, and it's the fix nobody wants to believe because it feels too simple. It really is that simple. Once that cable's in, the hub on the second monitor behaves exactly like the one on the first.