How many CPU's are you asking for it to use? Why do you want it to use more CPU's than it is using now?
Parallelism has its advantages, but it also has its costs. It is very possible that LabVIEW has decided in its compiler that it doesn't need to use any more CPU's than it is already using now. At some point the cost of using an additional CPU outweighs the benefit of using it.
