I had a nagging problem that was carry over for a few years. Not sure what the mental block was but I just couldn't approach it. It was not a quilting project. What did work for me was finding an amount of time I think I could stand working on it. It ended up being 12 minutes. So each day set the timer and worked on it for 12 minutes. Yes it did take 3 months to get it done, but I did finish it.
If you can leave your work out so you're not spending to much time just getting it out and putting it away, just pick an amount of time you think you can work on it. One step at a time and eventually, Ta Da it is finished.