If a reset (unplug the system, disconnect the battery from the system board and hold the power button for 30 sec) does not work, the system board needs replacement.  
Hello everybody, and welcome in my post. Hopefully someone will be able to give me an advice.  So I've spilled a coffee on my 7590 (i7 9gen.). Not too much, but that was enough to brake CPU fan. Everything was working fine, except this fan - diagnostic was giving CPU fan error. I've decided to disassemble and clean it - I've used toothbrush and isopropyl alcohol.After putting everything back together I've noticed that laptop has stopped showing any signs of life - no response for power button or charger. From YT I found out, that after disconnecting CMOS battery I should start it up and then on working system, connect CMOS battery. This is the second time when this happen to me - I had the same situation with XPS 9305 (i7 11gen.) but Dell technician who came to my company to fix few laptops, he managed to resurrect it. Unfortunately I wasn't there that time so don't know how he done this.I'm guessing that XPS's have some kind of protection, as I've never had that kind of problem with Latitude series. I'll be more than happy for any suggestions to try.Regards
XPS dead after disassembling