How much valves are in a modern day computer?

There are no valves in a modern computer. If by valves you mean vacuum tubes, the equivalent is a transistor. Modern CPUs have many transistors/gates on their dies. The SandyBridge i7, a near-top end general purpose computer COU can have 2.2 billon transistor elements on the CPU die. Of course there are many more transistors incorporated in the logic chips, controllers and video cards in a computer as well.