Dell XPS 13 plus 9320: Windows not starting

Dell XPS 13 plus 9320: Windows not starting:

1. Laptop was running fine without any issue.

2. I started support assist hopping it would free up some disk space. This time support assist UI looked new to me. 1/2 week ago all the listed updates were successfully done.

3. After 5/10 min (I was not in front of screen), I found screen is off and keyboard, mouse not working. Fan was so noisy at that time.

4. After 5 /6 mins, keeping power button pressed few seconds, I powered off laptop.

5. I turned on again. It asked bios password and I entered. After that display shows "secured with dell safebios XPS" and doesn't move. I waited long time but it doesn't move. I tried restarting this way several times and sometime the screen remains blank (no cursor) after bios password.

6. I tried running diagnostics quick test. Progress stops at 15% all the time during testing processor. I waited even 2 hrs to let it complete. Then I tried advanced test and run all items including processor test one by one successfully.

7. I can navigate through bios menu but display freezes within 2/3 mins. No mouse and keyboard works. Then I have to restart.

8. If I select support assist os recovery, it also end up with "secured with dell safebios XPS" screen without moving.

How to fix this issue please.

TIA