I agree with
@maflynn that this sounds like hard drive failure, so you will most likely need to get it replaced in the near future. Hopefully, you have some backups, as if you can't start from recovery and don't have backups then you'll most likely have to look at data recovery software/services to get any important files off the hard disk.
If you can start from the recovery partition, then start it up by turning on your Mac while holding the Command and R keys and you should get a menu that looks a bit like this:
Then click Disk Utility, then select your startup disk and then click "First Aid" at the top of the window. From there, you can check whether there are disk errors preventing your MacBook from booting. If you don't see your startup disk there, your hard drive has died and you'll need to get it replaced. If Disk Utility can't repair the disk, then you should first attempt to
back up (if you haven't done so already) by following these instructions (taken from
https://support.apple.com/en-us/HT204323):
- Connect an external USB, Thunderbolt, or FireWire drive to your Mac. The drive needs to be the same size or larger than your current startup disk. It also needs to be a drive that you can erase.
- Use macOS Recovery to erase the external drive, then install macOS onto the external drive. Make sure that you select the external disk as the one you want to erase. Don't select your built-in startup disk, usually named Macintosh HD.
- After installation is finished, your Mac automatically restarts from the external drive. When Setup Assistant appears, select the option to migrate your data from another disk. Choose your built-in startup disk as the source to migrate your data from.
- When the migration is done, complete the steps of the setup assistant. After the desktop appears, confirm that your data is present on the external drive.
Then, try to reinstall macOS onto your internal disk and then migrate the data from your external drive.
If you can't get into recovery then you'll need to get some macOS installation media because your MacBook is too old to use Internet Recovery. Probably the easiest way to do this would be to purchase a Mac OS X Snow Leopard disc (
https://www.apple.com/shop/product/MC573Z/A/mac-os-x-106-snow-leopard) then install it onto your hard drive if it can be seen by the installer (of course, if it can't see your hard drive it has probably failed, so you'll need to have a new one installed first). Then, upgrade to El Capitan (the most recent version supported by your machine) using these instructions:
https://support.apple.com/en-us/HT206886.
If you require a more detailed explanation of any of the steps please let me know. Hope I can be of assistance