After your entire post i understand that your main issue is that your PC hangs on Start Screen. Don't be panic as i have very effective and result oriented solution for you:
To boot into safe mode, please follow the instructions below:
Start the computer
Tap 'F8' on the keyboard immediately and every one second until the Dell logo screen disappears. From there you will see the Windows Advanced Options Menu on the screen. (If the Windows Advanced Options Menu does not appear, restart the system and try again.)
Select Safe mode with Networking and press Enter
Log on as the administrator or as a user with administrative access
Check Dell Latitude E6420 Manual- https://guideusermanual.com/product-name-latitude-e6420-manual&po=344640〈=English for more ideas.