The HS-750 is a plotter. One cannot print to it. It only cuts from a vector file. So either you are confused on terminology or what the plotter is capable of.
The correct setup for the plotter is to connect it to a serial port on your computer using the Gerber supplied serial cable. Next you open the GSP Tray and check your installed plotters. The icon should be among the icons at the right side of your task bar.
If it is shown as being installed, make note of the Com Port number and close it. If it is not installed, then click on the install link in the GSP Tray and follow it along to install the HS-750.
Once you are showing the HS-750 as an installed device, test it by sending a job from Composer to GSPPlot. It must have vectors. For purposes of testing, remove the blade tool from your plotter and send the job to the plotter from GSPPlot. This approach will save you from having to actually cut any vinyl. Sending the job is done by pressing the F8 key from your keyboard when the job is open in GSPPlot. The plotter should run if it is turned on.
Let us know if you need additional help.