Laptop experience

I bought a laptop on the 30th Aug 2022 since day 1 it hasn't been working properly. It's very slow and it keeps on freezing. I went to the store to report the issue and they said they can book it in to be checked and I'll be charged 15% of the total charge because I installed a password option. I mean how was I to setup my laptop? And on the ts n cs it says goods returned to them within 14 days of purchase they may consider exchanging subject to such goods are returned in their original packaging and in good condition. But when I went to the store they told me the opposite an worse thing is it was never explained to me properly.