Run Only One Instance - Exit If Already Running..??

I'm new to VBS and in need of some code that will allow only once instance of the VBS File to be ran at a time..
so if the 1st instance is already running, a 2nd instance cannot be ran...

Is this possible at all or not..??
If so How do i code it..??

i have don't know if there is a proper way to do this, but you could read the vbs file, delete it, then recreate it when you script finishes