Laptop not booting Dell Inspiron 15 5000 Series

What’s wrong:

laptop will not start windows, BIOS. Did get one error code beep

What I have tried so far:

1)motherboard swap (same problem recreated after swap)

2)RAM swap

3)Testing hard dive with SeaTools for Windows. While hard drive is connected externally to my PC, I can look at it’s contents and copy them etc. When running tests in SeaTools, I get a fail code of 6C9AC2A4. “

Serial number not detected, SeaTools did fail the drive,” as indicated on this page: https://www.seagate.com/staticfiles/support/seatools/seatools-test-codes.html

4)When turning on laptop, it only goes to a blank screen. Backlight does seem to turn on. An LCD test works (RBG all flashes).

5)Battery is believed to be dead. All of these tests are performed with the battery taken out and the AC Adapter plugged in.

Here is a video of the error code beep:

https://www.youtube.com/watch?v=jzSWsRQjf1Q

Any suggestions?