Hi - I have a custom rig (Intel Core i7-5820K, GeForce Gtx 980 Ti, AsRock Fatal1ty X99x Killer mobo) that I've been using with the Dell U3415W ultra-wide 3440x1440 monitor in Windows 10 for about 4 years (out of warranty on 11/24/18). It could be a little buggy (trouble waking from sleep mode, occasional flickering), but mostly worked fine.
As of last month, the U3415W shuts off when the Windows logo appears during startup. It will work in safe mode, but I can't edit video and motion graphics (my job) that way. I have tried absolutely everything - a Windows reset, a full Windows re-install, uninstalling and re-installing drivers, Windows repair, and 4 straight days with Windows technical support yielded no success. It works fine with other computers (a 2012 MacBook Pro and an old netbook), but the official response from Windows is that this is on Dell's end. Any thoughts? I'd really like to not have to replace a $700 monitor just because it's not communicating with Windows 10. Thanks!!
There is nothing Dell can do from a warranty perspective. I can offer some thoughts.
* My assumption is that you installed the Windows 10 1903 update which created the issue? If yes, have you considered backing down/rolling back Windows 10 to the prior version that worked with this out of warranty U3415W? * Did you check on the Nvidia Forum to see if the June 2015 GTX 980 Ti has newer driver compatible with Windows 10 1903? If an OS rollback were successful, you could install a newer Nvidia driver, Then retest 1903.