XPS 15 random shutdowns and missed restarts, manufacturer mode and caps lock stuck on

Hello.

XPS15 7590 here.

A couple of weeks ago my XPS randomly shut down in the middle of light office work. I could not restart it until I performed FLEA procedure and it turned on in manufacturer mode and with compromised audio drivers.

Now it keeps shutting down randomly (sometimes after a minute, sometimes it works for 24hrs no stop) and more often it cannot restart after being manually shutdown or asked to restart. It goes in manufacturing and shutdowns or even just becomes unresponsive/only turn backlighting on and then shuts back off. Sometimes gives out diagnostic LEDs, various combinations regarding CPU or bios error.

Only "solution" is waiting and trying again after half an hour or so.

Then after trying again manufacturer mode comes out and I have to cycle on off a couple of time to deal with that and caps lock light remaining stuck on. Stress tests performed, no issue found. Local repair shop says Northbridge damage but I suspect it could be related to previously known dead/malfunctioning ram slot now left empty.

Any clue on what I could try? Bios recovery? Clean install? It would feel very dumb to change a laptop which basically works for hours or days except some random periods or after shutdowns.

Thank you