How to know more than one instance of a Form is running or not?

Question

I have a Menustrip With 1 Menu Item Say Add Record.

When i click on Add Record Menu Item assume Form1 is opened.

My Problem is When i click on Add Record for 5 Times. it is opening Form1 5 Times.

How to open Form1 Once only even though i clicked for N Times.

Its the MDI form


Thanks in Advance..