My Screen Isnt Working On My Hp Pavillion Entertainment Pc But My Laptop Is On?

It's best to check first whether you accidentally pressed a button on the keyboard that tells the computer to send its video signals to an external device.  You'll need the manual to be sure of what that button is.

LCD screens (especially portable ones, such as on laptops) aren't terribly tough generally, and it is quite common for the screen to develop bad pixels (dead areas on the screen) or to blank out completely.  Even if you are out of warranty it is a simple procedure for a repair shop to source and fit a new screen.