If I understand what you mean correctly - that is, two computers, one printer and you wish the two computers to share that one printer - then you have two options:
1) Leave it connected via USB to one computer as you have at the moment. You can print to it from the other computer via your network - wired or wireless - but the host computer, the one with the printer attached to it, would need to be switched on when printing. Regardless of your setup, if your printer is connected to a specific computer, then that computer MUST be on to for it to print.
2) Get one of
these for your network. (Sorry mods, not promoting that particular retailer, just the best example I can find.) It works for your printer exactly like a broadband modem shares a broadband connection - any computer can use it and you don't need to have any particular one switched on for it to work.