Method not called from OnStart()

I have created a Windows Service in C# that I want to execute a method when it is started. Normally this is quite easy; put the code into the OnStart() method of the Service and make sure it's properties are set to "Logon as Local System Account" and "Allow service to interact with Desktop" checkbox is ticked.
I have done this but the code I have under OnStart will not execute.
It doesn't give me any errors (I've tried catching exceptions).
Basically I want it to fetch a global variable and use it somewhere else:

protected override void OnStart(string[] args)
        {

            System.Windows.Forms.MessageBox.Show("Important data is ");
            System.Windows.Forms.MessageBox.Show(MyProject.GlobalVars.ImportantData3.ToString());

When I do the above it just wont start the service. MyProject is the namespace,GlobalVars is the class and ImportantData3 is the variable.
I am only displaying the variable in a message box to see if it is getting it back as I want to use the variable later on.