I cant get Roller Coaster Tycoon to work on my laptop....?

I had installed Roller Coaster Tycoon on my laptop once before. When the trial ended, I uninstalled it. I tried to install it again with the disk, and it says I cant install it until I uninstall the old one. I have searched my computer for RCT, roller coaster tycoon, roller, coaster, tycoon, hasro interactive, hasbro, interactive, and atari. Nothing is found on my computer pertainging to Roller Coaster Tycoon. How can I get whatever it is on my computer off and install the newer one?