I have the Dell XPS 15 9560 and I've installed a new motherboard today. The laptop keeps shutting down randomly. Sometimes as soon as an intensive task starts (Unraring, opening 15 chrome tabs all at once, or any task that is demanding.) 

It shuts down sometimes after few mins and sometimes after seconds. The shutting down looks normal; I get "Shutting down..." screen and no errors or warnings.

Bios Version is 1.7.0 (even though the latest version on Dell's website is 1.6.2)

I've run Diagnostics (using F12 when the laptop starts) and all tests passed. 

Any advice?