It is not uncommon in problem solving to get stuck, and sometimes you get stuck many times. Problem solving is not a linear process (not usually). You go down a path using knowledge, thinking about what needs to be done, how it can/should be done, evaluate it (or someone else evaluates it for you) and you have to retreat or fix one or more issues before you can proceed. You can iterate and go back forth from almost any point in the journey to another point. The more challenging and more ‘unknowns’, the more back and forth. Here are some techniques for dealing with problems you are stumped by.
In some cases, there is no going forward and it is time to retreat or take a step back (you need to learn when to do this). You might be working on the wrong problem. You might have missed something, did not pick up appropriate assumptions or requirements. The retreating will vary - in some cases, you have to retreat a little and in some, you might have to start again from scratch. Moving forward, you might have a bunch of things ‘to do’ before you actually move forward. You might also find that a bunch of new tasks or future problems to solve were created. This is problem solving.
If you are stumped by a specific aspect, write down everything you know about it.
What is it similar to? In structure, form, construction, process, method, purpose? What happens if you think about the similar object/problem?
What have you seen or done that is similar? Talk it through - what did you do, what did you think of, why did you do something, what happened when you did it?
Sometimes look for repeating patterns or themes - what is the same. Sometimes look for how two bits are the same with respect to their differences. For example, you are looking at something involving students and a solution is evading you because people keep saying that ‘all students are different’. Usually there will be some things the same (that is the easy bit). Next, look at how they are different and the differences. Any patterns there?