2007 Macbook Pro will not boot to HDD
It appears that your drive is failing. Your best bet is to attempt to clone the drive to prevent data loss. If you're unsure how to proceed, your next best bet is to run fsck, which can, in some cases, fix any formatting issues on the drive (but NOT physical ones). This Apple support article will give you a good walk through of the troubleshooting steps, but again, best to try to rescue data if you don't have a back up before going forward.