How to troubleshoot inconsistent connection?

Hi all,

Sorry if this is a frequently asked question, I've got no idea what I'm doing both setting up and troubleshooting networks.

But, I recently converted my shed into an entertainment room, and obviously set up an ethernet network to use my computer out here. Net works fine, except the connection is very unstable. I seem to drop out super inconsistently, some days I don't lose connection, other days every minute or so I lose internet.

Basically all the info I know off the top of my head is;

NBN box (I'm aussie), goes into router, router goes into switch, switch goes into ~35 metres of cat5e through the roof, out into the shed, into another switch, then through the wall out to my computer.

Sometimes when I lose connection, on the network tab in the task bar it says connected to network but no internet connection, sometimes it says not connected to network, sometimes it says connected to network and internet connection, but I don't actually have an internet connection? most confusing part is every now and again, the switch seems to not be connected to the house (the indicator LED is turned off in the shed and in the house)

Now, I have no idea how to diagnose the issue(s) but I am willing and able to learn, I just have no idea where to start.

My apologies if this is a confusing post, or if there's not enough info, I am happy to provide clarification or extra information if needed.

Any help would be greatly appreciated, I plan on spending a lot of time out here and so I would love to get this fixed if possible.

Thanks :)