The operating system installed on the drive will need to be introduced to the new hardware.
What OS are you using?
If you are using NT, 2000 or XP you can run a repair installation and then reinstall all of your software once on there.
to repair the os you need to download and make the 6 boot disks from microsoft. Once the last disk is loaded there will be the option R that will repair the OS. You will probably have to reload all your programs.