Games don't work without tweaking

[blaze4eva]

Ive got a problem with some Pc games on my PC. For example Medal of honor: Allied Assault, i borrowed from a mate. It installed fine and when I went to play the game I clicked on the exe and nothing happened I kept on trying but no luck. So I got a crack off gamecopyworld.com allowing me to play the game without the CD and it worked.

Any reason why this game didn't work with the cd before i applied the patch.