Assuming you can eventually get to the desktop, try disabling fast startup in Win 10: Be patient at #9 because Windows Update may have to install some updates that can't be installed when fast startup is enabled.  When you get to the desktop, do another full power off shutdown.  Then power on and if the issue is fixed, you can re-enable fast startup in #6 because it will make future boots noticeably faster. If the problem recurs, disable fast startup again because there might be some additional updates that can only be installed when fast startup is disabled. As for the BIOS issue, when was last time you replaced the motherboard battery?  
Updated the BIOS from A11 to A14 and cannot enter the BIOS interface. I tried two ways: hit F2 or F12, or go through Win 10 to UEFI. Both ways failed. The screen keeps black and keyboard and mouse have no response. I am not sure if there is any software issue with the monitor and BIOS. For a normal desktop rebooting, my machine shuts down with "restarting", then black screen, then the blue screen with "please wait". In between, there is no any image showing up, including the Dell logo.  BTW, when I tried to install Intel HD Graphics Driver from dell, it failed and said "not validated " Any comments or suggestions are welcome. Thanks
XPS 8700, installed BIOS A14, cannot enter BIOS