[SOLVED] I need help with an Excel Checkbox.

Hello,

I can't get a checkbox in Excel to work. I know little VBA and can't figure out the code to accomplish what I need.
I have the Checkbox (Form Control) on the sheet and I created a UserForm to enter some data in it.
What I want is that when I check the box, it loads the user form.
I tried putting code in a module and linking the box to it, but it threw an error about a variable not set.
I don't know how to proceed.

This is what I used to open the form:

Any help will be appreciated.
Thank you.