Please list Dell model number and version of windows. Example: Dell Inspiron 3543, windows 10
In the meantime, type device manager onto search box, stroll down to Display Adapters and expand it. Right click video driver, select Uninstall (do not check the box that says delete driver) and restart the computer. This should refresh the driver, hopefully there's no more flickering .
If refreshing the video driver doesn't fix the issue:
Please use the System Restore tool on the computer. The tool should bring the computer to an earlier time before the flickering problem occurred.