Orbi - weak signal strength and invisible network for one computer

Hello, new to the Netgear community here. Just bought an Orbi with 1 satellite after suffering from weak connection with my old TPLink router with 1 booster. However, I'm still suffering from weak signal strength and one of my older laptops (5+ years old) cannot find the wifi network. I'm not very sophisticated at home networking etc. and would appreciate any help here.

1. Laptop which is 5+ years old running Windows cannot find the wifi network while our other newer devices can. The laptop can connect to the internet when plugged in directly to the router. Is this to do with an old wifi card for the laptop which cannot receive the frequencies being put out by the Orbi? Any way to solve this?

2. I used to have a TPLink router with one booster in the bedroom. I live in an apartment over two levels (bedroom and router on lower level). Reception was fine this way in the bedroom, but signal was non-existant upstairs. I have now set up the Orbi router in the middle of the living room as before (lower level) which is where the modem needs to be. However, around 10-15 metres down the hallway to the bedroom and after one bend, reception is nearly nonexistent (note: although 'down the hallway', the Orbi is inevitably tucked a little behind a wall). I have placed the satellite halfway up the stairs which lead up from the living room, where the signal strength was 'orange'. I tried moving the satellite higher up the stairs so that it is more directly above the router in the living room, and signal strength was also 'orange'. I've tested internet speeds to be 50mb/s next to the router, 5mb/s next to the satellite, and when 10-15 metres from the satellite in pretty much open space and just 1 bend, I am getting under 1mb/s. This doesn't seem very impressive, which I'm quite surprised given so many reviews say this has improved their signal strength by a lot. I have only set up the Orbi based on out of the box set up instructions. Are there settings which I need to tweak which could improve its signal strength? Connectivity is also not very stable, especially after an update to the firmware just now, which has led me to lose internet connection 3 times while I typed this post (and had to retype this once since I clicked 'post' without internet). Turning off and on my wifi on my computer resolves connectivity.  

Many thanks in advance!

Edit: Forgot to add in my re-type that I often receive many other peoples' networks but not mine. It's quite cluttered with networks given it's an apartment building. Strangely I receive someone's 'Netgear 2.4ghz' and 'Netgear 5ghz' network better than my own network a lot of the time and places at home...