Apparently, you did something wrong or incomplete. The usual thing to do after installing a new hard drive is to make a full copy of the old one, which results in a fully working system with all your programs and data saved.
If, however, you did a reinstall of Windows you might need to reinstall some drivers yourself. In your case, this seems to include the correct drivers for the sound card. Doesn't the system complain at boot about hardware without drivers? Does the New Hardware Wizard detect a device without driver? What does Device Manager say about the card? And did you install the Multimedia part of Windows? What does Control Panel>Multimedia tell you?
Without knowing details of your machine (what motherboard and soundcard), your OS (Windows 95 or Windows XP), what you did and didn't do and settings of Device Manager and Multimedia, this is about all that can be said about the subject.
Hope this helps.
Recently installed new hard drive on my computer, now I have no sound at all.