Yes it will cause you problems. The ps system is made to have ps fluid in it while the car is running, using the ps system without the fluid circulating through it will cause the gears inside the power steering to chew themselves up. You want to convert to MANUAL steering, and I hear the parts for that are not only hard to find, but it's a pain in the ass to install. But yeah, I would recommend against just disconnecting the lines to your power steering.