HP PSC 750 printer will print only half a page

Answer 1

 The problem is with the printer not scanner thats why when you scan some thing the result is 100% and when you print out some thing you don't get the required result out from it. So you need to change the Cartridges of the printer and your problem will be fixed. As you said its all in one but still ink for scanner and printer are differently placed in it.