I believe I've found a fix for the distorted screen / graphics getting messed up on the Dell XPS 13 (L321X) after upgrading to Windows 10. The trick is to delete the current and previous versions of the Intel HD Graphics 3000 driver from Windows 10, and then reinstall it using "compatibility mode" set to Windows 8. (This should fix the Windows 10 distorted screen on other laptops/computers too.)
You may want to print out these instructions to refer to while you are applying the fix.
Here are the exact steps:
1. Download the latest driver for the Intel HD Graphics 3000 from the Dell website (type in your service tag and go to the drivers download page, it should lead you to this file). (The driver filename should be "XPS-L321X_Video_Driver_RGC4M_WN32_126.96.36.19929_A00.EXE".)
2. Turn on airplane mode on your XPS 13 (L321X).
3. Go to Device Manager, then:
4. Open File Explorer and right-click on "Local Disk (C:)", then:
5. Now, with airplane mode still on, you may restart your laptop. The default Windows 10 display driver will kick in and your screen will default to a lower resolution.
6. Find the Intel HD Graphics 3000 driver installation file you downloaded in Step 1 above, then:
7. Double-click on the Intel HD Graphics 3000 driver installation file to start installing the driver. Leave the box checked for "Automatically run WinSAT and enable the Windows Aero desktop theme (if supported)". Let the installer finish installing the driver.
8. Select the option "Yes, I want to restart this computer now" and click the "Finish" button.
9. After your laptop restarts, you can close the WinSAT command line window if it doesn't close itself.
10. You can verify the Intel HD Graphics 3000 driver has been reinstalled in Device Manager, and you can turn off airplane mode.
11. Enjoy your "new" Dell XPS 13 (L321X)!
This should fix the distorted screen / graphics messed up problem for good in Windows 10. At least, it's been working for me for quite some time now. Hopefully it fixes your XPS 13 L321X also!