vb.net - A function is blocking the all application from being used until it has been executed -

I have a function that performs a big operation, when I call it, it is impossible to do any other operation is.

I tried to think of a representative if I call me. The new mydelegate (myfunction ad) allows it to solve the second part of the application that it is being executed but it does not work.

How can I do that when I call the function (when it is being executed) is accessible in the second part of the application?