I have a tough time concentrating on hard problems too. I don't have ADHD, I'm just scatterbrained and easily distracted. When I do hit that "zone" I can stay in it for hours, but I rarely get to that point on any single problem. Here are some things I do:
Go for a walk. Don't face the problem head on specifically, just absorb the gist of the problem and then go for a walk and let your sub conscious deal with it, then about half way through your walk, start talking out loud about it. This works well for me when I'm stuck on something.
Learn what real problem solving is. Look up the Wikipedia article on Troubleshooting, it's fantastic and has some great insights.
The main thing about problem solving is not to be overwhelmed by the entire problem. Break it down into its most basic forms, and then solve a part of it, then work toward the solution. Don't try to build all of the solution at once. Iterate toward it. It works.
Go for a walk. Don't face the problem head on specifically, just absorb the gist of the problem and then go for a walk and let your sub conscious deal with it, then about half way through your walk, start talking out loud about it. This works well for me when I'm stuck on something.
Learn what real problem solving is. Look up the Wikipedia article on Troubleshooting, it's fantastic and has some great insights.
The main thing about problem solving is not to be overwhelmed by the entire problem. Break it down into its most basic forms, and then solve a part of it, then work toward the solution. Don't try to build all of the solution at once. Iterate toward it. It works.
HTH YMMV.