AFAIK suffix ".cpr" (Cubase Project File) was introduced with SX1 since 2002. Pre-2002 VST projects will have an ".arr" or an ".all" suffix.
Your files should all have natively the suffix .cpr; so something was going wrong during the transfer from one system to the other one I'm afraid. Are you sure that your files were not encrypted by a third party mechanism on the original drive ?
Have no idea of what you can do.
Nuendo 6.x, Cubase 7.x, Wavelab 8.x
PC A:Win7x64 / GA-P35-DS3P QX6850, 8G DDR3 / 2xRME Digiface / 2xPowercore PCI MkII & Firewire / MCU Pro
PC B:Win7x64 / GA-880GA-UD3H X6 1090T, 8G DDR3 / 2xRME Digiface / 2xPowercore PCI MkII & Firewire / MCU Pro
PC C:Win7x64 / P5QSE Q9650, 8G DDR2 / RME Digiface