S2721HGF, no display

If the monitor is inside 30 days from shipment, call and have it replaced or refunded. 

If it's out of the return period, call for a warranty replacement.

Contact Dell GHN (Get Help Now) chat technical support Monday through Friday. Click the blue "Get Help Now" on the right to start a private live chat session. Share the private Service Tag with them so that they can verify the ownership and warranty status. This will also generate a unique Technical Support case for your unique Service Tag. If already out of warranty, click here for the Dell out of warranty offerings.

As far as troubleshooting, the only thing I can think of trying out here if you haven't done so already is a hard reset:

1. Disconnect any external devices including the power cord
2. Hold the power button down for 15 seconds 
3. Bypass any power strips, surge protectors or battery backups
4. Verify the wall outlet is functional
5. Reseat the power cable into the monitor
6. Attempt to power on the unit

Odd that the monitor is detected in the OS but you're not getting any other signs of life. The only other firmware you could try out would be this driver, but it seems unlikely to make any impact. Since the monitor is detected, then its possible the panel itself has gone bad, yet, the controller may still be good. It sounds like the OSD does not even open, but you could try to reset the factory defaults off of best guessing the menu to see if that possibly gets video back. Click here for the user guide and to check out the possible path for the menu. 

Otherwise, if there isn't any response from the monitor then it does seem like it would be a dead monitor. Now if you really wanted to try and repair the monitor, here is the service manual. However, this typically isn't really cost effective since you still need to buy a working panel. It may not even work after this too, so buying a new unit is likely the way to go. 

@ejn63​ My waranty just dropped like 2 months ago the screen was a gift i bought with the 13rd months of work benefit, I already call it once at the start and got the same screen just with a new cable but change nothing 

@DELL-Daniel V​ I already done that i got it to do hard reset, soft reset, i disconnect it for 2 hours, connecte it back but nothing i open it, because my waranty is already past, and check voltage, power supply okay, but no power to the video capture card and i think from what i saw that i can't buy one video board, To be more clear i tried 3 cable, all work for another screen i test the power board not problem the only preblem that i saw is the video board

@Alexandre Guahcer​ 

These ship with a 3 year warranty - - is the monitor that old?

@ejn63​ Yep bought it in december 2021... 

@ejn63​ I got i think 2 more  years of waranty when i call for the first time but today no waranty till 2025