If you say that you've done the calibration properly, and that the other PC did not exhibit the same symptoms, it could be related to grounding of the PC. You could try to ground your radio using a long wire with crocodile clips on both ends. Hook one clip to the neck strap and the other end to a gounding point e.g the metal casing of your PC.

On the installation sequence, it should be main disks.....addon1......addon2......addon3......addo n4......addon5.....patch. If you need to uninstall and reinstall, follow the instructions at the bottom of this page http://www.aerofly.com/afpd/downloads.html