The usual reason for the sound not working on a computer which has just had the hard drive replaced or formatted is that the sound driver hasn't been installed.
If the motherboard in your laptop uses 'on-board sound', the driver will be on the motherboard set-up disk which should have come with the laptop. If your laptop uses a separate sound card, there should be a disk associated with that card.
If you've not got the relevant disk, you'll have to download the driver. It's probably available here:
http://uk.computers.toshiba-europe.com/cgi-bin /ToshibaCSG/download_drivers_bios.jsp?service= UK&banner_id=C_DOWNLOAD_FILES
Chris