To test the device directly at the place of issue, I propose this method.
When you start the device, as soon as the round Dell logo appears - press F12.
This menu should appear:
Select Diagnostics, and wait for the result of the test.
Sometimes questions will pop up (are the bands visible, has the sound worked, and so on).
In the end, you will be asked whether to start the test of RAM (takes about an hour) - you answer at your discretion.
Upon successful verification, a textbox will pop up
In case of errors - there will be a corresponding notification.