AC1200 cannot connect to WIFI network

First - you need to understand that to utilize the latest WiFi standards - BOTH ENDS - ie the router and the client MUST meet those standards, an 802.11n router (which is what you have) with an 802.11ac client will not, can not, deliver anything better than 802.11n performance. A Dell XPS17 should ship with an 802.11n wireless card, so you can expect 802.11n performance there, and there's no reason to expect that switching to a Netgear client would provide any significant improvement in performance. Second - due to the laws of physics - higher frequency transmissions suffer attenuation to a greater degree - 5GHz networks will generally have less range than 2.4 GHz networks - depending on your distance from the router and also what lies in between your laptop and the router - your very low 5GHz signal strength may or may not be expected.