Sounds like the CMOS battery is dead. This page refers to your laptop specifically: Dell Latitude E7240 Ultrabook CMOS Replacement But this one is far better and should give you what you need: Dell Latitude 7490 CMOS Battery Replacement Dell guidance here: https://www.dell.com/support/kbdoc/en-us/000135178/how-to-replace-a-cmos-coin-cell-battery-on-your-dell-notebook Best of luck