There are several reasons behind the inaccessible boot, including corrupted or damaged boot partition on the hard drive, damaged or incorrectly configured boot loader, malfunctioning or failed hardware components, such as the hard drive or RAM, and so on. The inaccessible boot can often be fixed using a diagnostic or repair tool, such as the Windows Startup Repair Tool. If the problem persists, it may be due to a hardware failure, wherein you will need to get a new one and reinstall everything.