There's a new QA engineer at work who just joined this week. He's a pretty typical hire for me - lots of talent, lots of potential, in just a bit over his head. He came to me Friday with a task he'd been given, and he just didn't know how to approach it. The problem was that he was starting at the beginning, didn't know how to do that part, and so was stuck.
The trick with a problem you can't start on is that you don't have to start at the beginning. Start anywhere you can get a toehold. From there you can work your way back to the beginning and forward to the end.
I don't care if you can't solve the whole problem now. Don't beat yourself up for it; that's a recipe for getting nowhere. Just solve the part of the problem you can do.
So, when you're faced with a small problem, just find yourself one small toehold and remember that any change you make is fine, as long as you make it just a bit better than it was when you started. Launder, rinse, repeat, and eventually you'll have nailed the whole problem.