Make sure the drive is registered in bios. you also need to make sure your master boot record is intact. Sometimes placing your windows disc inside the computer, booting from it and promting for a repair can fix this problem.
If you still can't recover your data after looking into the BIOS - do not do anything else, as you may damage the data you're trying to recover.
You can take the machine to a local computer store where they can extract any data from the drive for you and put it on an external disk.
Many many people try to reinstall windows or use a recovery option, which actually wipes out their data.