While I lack the many years of life experience you have, I can certainly relate to the feeling of losing passion for "my main trade". As far as I know, the most solid remedy is to simply do something else for a while. This will:
- Break up the tedium and give your mind some breathing room to rest from 17 years of focus.
- Teach you to better appreciate the nice things about web programming. For example, straightforward distribution to users, far fewer headaches in supporting legacy users, relative independence from user system unlike desktop applications. After a while, you may start to miss the job you are now disinterested in.
- Remind you that if you're so sick of web programming that you have to give it up and find another career, it's not the end of the world, because hey, it's not like you can't do this other thing, too.
- Gain you a new, valuable skill that will improve your marketability and broaden the spectrum of projects you can readily attempt.
Often, when you do something you love for many years, and then one day start feeling like you're sick of it and never want to touch it again, you're not really sick of it, and you don't really never want to touch it again - you just want a break. I am reminded of a short bit from Jonathan Haidt's The Happiness Hypothesis where he talks about surgeons who go on vacation to Haiti to escape the stress of their jobs, only to start volunteering at the local hospital after a few days out of sheer boredom.
As for what exactly you will do, it really depends on your personal circumstance and preference. You can try:
- Things related to your job: Server-client software, web scrapers, network administration, browser games.
- Things vaguely related to your job: Developing software that has little to do with the web, contributing to open source projects, (desktop) game development, solving computer science exercises from a textbook or the Euler Project, trying your hand at an AI project.
- Things completely unrelated to your job: Start an exercise routine, volunteer for a local charity, learn a language, get into a new sport, learn to play an instrument, join a local dancing class, start working on your long backlog of books or films, make a garden if you have a yard, try to do some DIY home maintenance.
It really doesn't matter what you do, so long as it interests you and and feels appropriately challenging (you don't want something effortless, but you also don't want something hopelessly difficult). It doesn't even matter if you ever get good at it - it's a hobby; being good is not the point. In fact, it is crucial to not get carried away and start stressing out over how much better some other people are at it. You're not competing with them.
It is preferable to pick something that is productive rather than a complete waste of time. However, it's not necessary: Once again, your objective isn't to become the master of your hobby, but to give yourself a break from work. Moreover, often it's impossible to predict what skills will come in handy one day. The rule of thumb is that if you're learning anything at all, or progressing in some fashion, you're doing fine.
If you don't have the luxury of taking a break form work entirely, such as a vacation, then the occasional evening or some time on the weekends will work just fine. If you are so overloaded with other pursuits that you have absolutely no time left over for a hobby, this is probably part of your problem.
Lastly, in the event that nothing excites your attention, consider that you may be depressed. Then, the issue is not with your job, but with you. If you are, indeed, depressed, chances are that there is no worthwhile activity that will be interesting to you. Such is the nature of depression. Regarding this possibility, you should really seek professional help (or at least research the topic from reputable sources). However, be wary of hypochondria and self-diagnosis - don't make trips to the therapist your hobby!