So the issue here had nothing to do with a
PictureBox or a
Click event but was purely because you were trying to use a default instance of a form in C# when that is a VB-specific feature. What you posted in post #6 is what you should have posted in post #1. If you have code that doesn't work, ALWAYS show us that code.
For the record, the vast majority of experienced developers will tell you not to use default instances in VB either. They exist primarily to allow VB6 developers to use forms in VB.NET in essentially the same way as they did in VB6 and they also allow beginners to access forms easily across a project without having to understand the principles of OOP. It's actually better that you learn the principles of OOP sooner rather than later and treat forms as objects like any other. I've never heard any C# developer say that they wish that C# supported default instances so there's clearly no actual need for them.
For more specific information on default instances, you may like to read
this.