2004 grand prix hard steering but no leaks and full of fluid

SOURCE: power steering fluid on grand prix

You should add it to the power steering pump reservoir, which if you have the 3800 series II its behind the engine on the passenger side.

SOURCE: 1997 pontiac grand prix gtp power steering

sounds like belt tensioner may be going . would make sound, & effect anything run by belt including temp.

SOURCE: power steering stopped, fluid level

return line on rackanpinion needs aclamp

SOURCE: where do i add power steering fluid?

Add steering fluid in the pump reservoir. It is located in the left side of the engine. see picture..

SOURCE: 1998 Grand Prix GTP windshield washer (full) not pumping fluid

Not difficult to remove inner fender liner (screws around wheel well opening and sometimes a few more)
Pump is available from most auto supply stores and easily installed in tank. Check power at the motor before removing it to make sure the motor is bad and the problem isn't somewhere else.(if no power there problem can be solved as easily as using a push button to get it powered up and as complicated as replacing the multi-function switch...pretty much your choice)