First, you should have a bootable USB drive with your OS (x32 or x64). Try to test it on another machine to be sure that it starts properly. Then boot from it, test the HDD state (e.g. checkdisk from command line) and try to use OS recovery. It may be reasonable to remove the battery and use the AC adapter only, because battery failure may prevent OS from working.
By default, options to look at the HDD content from boot media are quite limited. From my practice, I usually add Total Commander (the whole directory of its installation) to USB drive. This allows to run TC from command line; it requires minimal OS support like Windows PE on booting media. Sure, you need to add the appropriate TC version (x32 or x64). After boot, go to command line, change a drive (X: by default) to your USB (e: for example), go to TC dir and run it (totalcmd or totalcmd64). TC allows to look at HDD content more easily, make some fixes and copy your important files to external media.
But the main options are the system restore, HDD boot repair if OS is unable to begin to boot from HDD normally, or, if all that was unsuccessful, re-installation of the OS with keeping its current settings. Of course, if you have an HDD controller failure, nothing will work and you will not be able even to see the HDD after booting from USB and the option to (re-)install OS will not work. Need to replace of the main board or whole PC. HDD only failure is less worse because in many cases it can be replaced without sending the device to service centre.