Inspiron 5423, motherboard replaced, password needed

Hi from Athens, Greece

Brief story: Imagine you own a laptop that suddenly, one day, requires a password to work even though you never set one.

Long story:

So, my brother purchased a Dell laptop back in 2013 when a motherboard failure occurred about 3 weeks after the purchase. No prob, it was replaced under warranty. Everything worked fine until two weeks ago when suddenly the Anti theft screen appeared requesting him a password in order to continue the boot up sequence. BIG problem, no password was ever given to him. What to do next? After searching the web without finding any solution, he decided to contact Dell Greece.

To begin with, Dell technical support told him they couldn't find in their system that this laptop had a motherboard replacement (QC?). Thankfully, my brother had kept the mobile numbers and names of the two technicians back from 2013 and we provide them to DELL all the info.

Of course, no password was provided by DELL and the solution proposed was to replace the motherboard. 

Why should he pay to replace the motherboard? He didn't set the password, he didn't even know this technology existed. After all, its a replacement motherboard he couldn't have set a password.

What is more irritating is that the head of technical support told him on phone that he should buy a new laptop because "after all Dell Inspiron have a life expectancy of 5-6 years". So, If we want to keep a laptop for more than 6 years, Dell is out of the question? Is this official? Any help will be highly appreciated.

ps1 It appears there is no Dell Quality Assurance in Greece or a department to complain. So, I cannot escalate the problem nowhere in Greece

ps2 Even if I want to buy the new motherboard I can only find it in Dell USA, they told me that Dell Europe don't ship this item. "they have different policies".