I'm not completely stupid. I used to be a decent programmer. I'm now a halfway-decent programmer. I'm unable to make any progress, and my ability to hold a job of any kind is dubious. What am I doing wrong?
Hard to say, but a few key pieces of information might lead you in the right direction. Is the inability to make progress project-specific? You can test this by doing something small on the side. Is it accompanied by an "ugh field"? Do you have non-programming-related signs of depression?
P/S/A: There are single sentences which can create life-changing amounts of difference.