My Printer want stop printing!!!!!!!!! (by 2 users)

I had to change my ink and i kept clicking print to get the screen to come up to where I could get the cartridges out and now it want stop printing every time i turn it on it prints and I hit stop and cancel and it still does it until i turn it off or take out the paper i was wanting to know if there was some file I could open to cancel previous jobs because there's a lot I'll need more ink before its through. I have a epson stylus cx7400 and it keep saying enter a valid product i didnt see it so I just picked one close enough