A 7000 wifi adaptor cannot detect 5G network anymore

I've used my wifi adapter to connect to a 5G internet network. At some point, my girlfriend unplugged the cable that was going through the wall to the router and replugged it. Since then my device couldn't detect the 5G network, and could only connect to the 2.4G. Also I keep on losing the wifi periodically since then. All the other devices can connect on the 5G as before. Here are the things that I have tried so far : 

- Connecting and deconnecting the adapter physically

- Uninstalling the driver, and reinstalling

- Uninstalling the Netgear connection software, and work directly with the internet detection of my computer. 

- Unplugging and replugging the cable that led to the router. 

It should be noted that i do not have access to the modem : it is shared among a couple of persons living in my building, and belongs to the owner. I also cannot "open" the router box, which is sealed. I have had the product for 3 months now, so I doubt that it is because the product is "too old". 

I checked in the forum, and not much of the topics have been helpful to me, but it does seem to be a recurring issue. I work from home and would really appreciate if you could support as soon as possible. 

Thank you for your help