Hi,
This [https://www.dell.com/community/Laptops-General-Read-Only/Latitude-E6540-screen-problem/td-p/5165727|link] may be of relevance to your problem.
You can also perform a [https://www.dell.com/support/article/us/en/04/sln127964/how-to-troubleshoot-display-or-video-issues-on-dell-laptop-lcd-panel?lang=en|video stress test] using ''Dell SupportAssist'' (scroll down to find the link on the page), to check if there is a hardware problem.