My hard drive died, and I lost P-shop. When I tried to re-install it said the disc was blank, which is maybe some automatic protection so it isn't re-used. Is there any way to reinstall without purchasing again?
No, there's nothing in terms of 'protection' that prevents the disc from being used more than a certain number of times. The serial number on the CD case is what is used for activation, which is limited to two of your personal computers. As long as you have that, you can download the trial of Photoshop CS5 (if that's the version you own) from Adobe.com to install and then enter your serial number to activate.