A couple of additional thoughts:
1. If the laptop was stuck in Airplane Mode then, rather than following any suggestions from within Windows itself (or from the Microsoft website), you should have consulted Dell's website, as per my link here:
https://www.theanswerbank.co.uk/Technology/Question1784170.html
(It's clearly a known problem with Dell machines).
2. Assuming that you're in the UK (or in the EU), the retailer who sold you the machine was legally responsible for fixing any problem that occurred with it due to an 'inherent fault', without charge. Within the first 6 months after purchase, there's an automatic legal assumption that any problem that occurs must be due to an 'inherent fault' (which relates to something that was wrong when you bought the machine, such as a hard drive that's not up to standard).
Given that the problem seems to be well-known though, I still find it hard to believe that there was anything wrong with the hard drive. As I wrote in a previous post, far too many (so-called) computer technicians resort to reinstalling Windows (or, as in this case, replacing the hard drive) when they can't work out what's gone wrong.