Why it's so hard to find a job I like

I've been doing the same computer-type job even before I graduated from college. I used to really enjoy it, and sometimes I still get a kick from solving a problem or learning something new, or figuring out a way to do something better. But these don't happen as often as they used to, and now I spend a lot of my time doing the same things over and over again. I'm also so good at managing my time that I often don't have anything to do for parts of the day. So I've been thinking that maybe I just need to find something new. It would preferably be something that lets me use my extensive background in the work I've been doing all this time, but it would be different enough that it wouldn't just feel like the same old stuff. I'm not sure these jobs exist. I saw one at a company that seemed promising, but they pulled the job from their careers page (and I never even got an official "No thank you" from the company). I just saw something for another company, a start up this time, which I'm sure I could do, but my resume wouldn't necessarily indicate I'm qualified for. I'm leery of working for a start up though, since I'm pretty concerned about work-life balance, and I like to be able to do my own things on my own time, without having to worry about work interrupting at any time.

I actually have a phone screen later today with another company, but it's not the company I work for now that's the problem. I think this job will be basically the same as the one I have now, so while I'm open to interviewing and looking around, I wouldn't leave for just another job that's exactly the same as this one. No, what I want is something that probably doesn't really exist (people who have my job are just supposed to keep doing it forever, I guess, or go find something related enough that it's still not really what I want to end up doing). Oh well, there's always a barista job at Starbucks.