Just bought Flight Simulator 4 (also have Simulator X with no problems installing). The 3 CD's will install fine; however, the 4th disk will run for a while and then say "either the disk if full or is in use." I have 144 G left, so it's not the disk. I am not using it. The computer is connected to AC. What is the problem? I'm not too savvy on a PC; I'm a Mac user. Thanks.