In many ways I'm already screwed. By my own admission I have no marketable skills. Most of what I do is just putting PCs on desks and cabling them up. The odd driver install. Stuff that most anyone can do.
What really depresses me is that I can't envisage a route from where I am now to somewhere better. I'm looking at jobs right now, on IT job sites, and they all want real skills which I don't have. I mean sure I could apply for all of them, but what's the point? If they want a C# developer with 2 years commercial experience then I'm not going to walk in there and start talking about how many PCs I've put on desks.
Firstly, stop looking at software development jobs. You're not a software developer, so those jobs are not suitable for you at this time. Maybe that's the direction you'll move later, but (at least) a little experience with development will be required.
Start looking for IT Support and Operations jobs. Is it
really the case that all you do is plug in cables and install drivers? I'll bet it's not. Make a proper list of every task you do, or are responsible for, in your daily job. What kind of software and hardware do you install and maintain? How many PCs do you set up - are they part of a network or domain of some kind, do you have any responsibility for maintaining that? Have you ever stepped out of your comfort zone in some way - what did that teach you, and have you applied the knowledge since?
Your first step can be a small one - look for some jobs that are similar in nature and pay to what you do now, and apply for them. Do some proper research into the company and role, write a proper CV, and - if invited - prepare for and attend an interview. You'll be amazed how much this process will teach you about what skills you have, what you're interested in, and what others think of you. If you get an offer, all the better!
(GD, by the way, is actually a pretty good place to get advice on writing a good CV!)
It seems hopeless and yet despite that I have to somehow find a path out of this mess. And yes, it's a mess. I know this already.
It's not hopeless but you need to establish
what you want. I think you're stuck in a funk; you're living at home, working a minimum-effort job with a decent wage for what you do, and you've got too settled into your life to change it. My advice - you need to change
something to get you kick-started. That's why I think you should move out. It doesn't matter that you don't want to rent forever, it doesn't matter that it will be a little more expensive for a while (you have the money!) The point is to challenge yourself to think a little differently, and to get out of the rut you are clearly stuck in.
I don't think you should up and quit your job and go travelling - maybe that's what you'll end up doing eventually, but you need to find the passion for it, or for whatever it is that drives you in life. Beyond, I mean, having a pet - I completely understand why you want one, but it's important to have other goals too!
