That depends on what "more" means. :-) If "more" is a constant (finite) number then it means that you solve a finite number of NP-complete problems - which is still NP-complete.

Thank you Professor Michael Patiksson. Yes, "more" is a finite number :). Would you please explain the mathematical logic behind this? 

Besides, Can you kindly provide any example of a problem which consists of several Np-Complete problems in real life? 

I'd say if the finite problems are independent then the complexity is still the same...

@Ahmed, what about if they are dependent? 

Shamsur, you may continue this interesting philosophical discussion. But it will be useless until you show your concrete interesting example. You said that the problems are dependent. But you did not say about the degree of dependences. I think, you understand that this is important information.

It depends on how you are combining the two problems. Call the two NP-complete problems x and y. For example, if you want to know if both x and y are yes-instances, you still have an NP-complete problem (guess witnesses for both x and y, and if they verify both, you accept, so you have an NP algorithm for the combination). If you want to know if x is a yes-instance and y is a no-instance, you're probably outside the class NP, but you're in a class known as DP ("difference" of two NP-problems). Bottom line, the answer depends greatly on the formulation of your question. For starters you may want to look up "Boolean Hierarchy" in wikipedia.