replaced the hard drive but still getting error icons.

I have recently replaced the battery and hard drive in my iPod Photo. After charging it up and connecting it to the computer it doesn't get recognised by itunes and comes up with the sad iPod icon or sometimes the '!' folder icon which is the original problem I had with the old hard drive that led me to replacing it. I have put the iPod into disk mode and connected it to the computer but still no joy.

Does this suggest that the new hard drive is faulty?

Is there another reason i'd get those icons?

Any suggestions or advice would be welcome.