Hi there and welcome to the forums:)
I saw your post about trying to install and use your PSC 750 on your new Windows 8.1 system. After checking the drivers out for this printer, I have discovered that there is no driver available for Windows 8.1. Perhaps try running the HP Print and Scan Doctor to see if that will help with printing. If not, I would then suggest looking into an upgraded printer which will have more up to date software and would most likely function with 8.1.
HP PSC 750 All-in-One Printer Drivers
If you were to call HP, they may have a trade in option for you, if you're interested, I will include their contact info.
If you're calling within North America, the number is 1-800-474-6836 and for all other regions: click here.
I hope you found this information helpful!:)
Enjoy the rest of your Tuesday!