I'm still new, but am using the Coopers kit too. I've read a lot on the internet recently about our Coopers kit and kilo brewing, and the most common advice about whether to ditch a brew gets met with "be patient!" Way behind, but the next common advice is see if the hydrometer is working/being read correctly, and way, way in last place is a real reason the brew has stopped early or never got going, which is still fixable for the most part.
With the hydrometer, there are a couple of things to keep in mind. The readings can be off quite a bit due to gas, and I've seen this in my small experience. I took advice to pour the sample from one glass to another 10-20 times to de-gas the sample, then pour back in the tube and wait a few minutes, then take the reading, worked well for me. Also, every now and then, test some cool tap water and test that. If it's not reading 1.000, then you may have broken the hydrometer, which apparently isn't hard, try to be gentle with the hydrometer when moving it around/cleaning it.
But while it's hard to completely kill a beer, it's not hard to make a poor tasting beer. Every small mistake can cost you some taste, but for the time being, focus on the big topics like sanitisation, temperature control (especially over the first 4 days) and not rushing anything. My idea is to make these kit and kilo beers for a while, but really try to improve the process every time, which I am doing so far. When I can make a nice beer a few times in a row, I plan to delve deeper into more advanced techniques, but I'd rather not rush it, as I have no need to at this point.