Kind Attn: X-Box Gamer. Please help me out.

Question

I am developing an application where in i have to lock a perticular PC from external usage. This locking is done from a different PC on the network. Now my problem is to mask the Keypress (KeyUp, KeyDown) events. If the keys pressed are single i.e any of the keys on the keyboard, then I can set the "e.Handled" bool value to true. But when combination keys are pressed, i am not able to detect and mainly MASK them. For example if the user presses Alt+Tab, before the event gets generated, the Application control is shifted. Please let me know if you can some how mask such combination keys being pressed. Thank You.