I would suggest you to make method static. The problem is that all the content of them stays in the memory until you close the application.
So use static only if really needed (or for some small methods).
About your question, it would be good to share the code with us, so we can explicitly see whats troubling you.
Static members and methods are instance independent. Internal members and methods are only accessible within the current assembly (similar to protected, but even derived classes outside the assembly cannot access them).