If drive is not detected in Bios, try opening it up and checking the connection to the drive. SATA connector may be loose, try re-seating it. If it is PATA connected check it is pushed all the way into the slot. You should also be able to hear it spin up when you power on the laptop. If it seems to be spinning, making noise, you may have a bad boot sector. Depending on what version of Windows OS you are running there are different recovery methods to rebuild the boot sector.
for Windows XP see: http://support.microsoft.com/kb/307654
using the "Fixboot" command.
Windows 7 and vista see: http://support.microsoft.com/kb/927392