Possible Start-up Issues
If you are unsuccessful in booting from Safe Mode or any other bootable media then the problem is a hardware problem. Otherwise there may be a problem with the registry. It may even be as simple as someone deleting system files from the root directory (they should be hidden, but it does happen!). When floppy disk drives were in widespread use, a common problem was for a user to have a floppy disk in the computer when the system was starting. The system looked for the NTLDR program on the floppy disk and caused a fault stating 'boot failure cannot load NTLDR'. This problem was simply resolved by taking the floppy disk out of the drive and rebooting the PC. However, although this solution may seem simple and straight-forward to a technician it may not be to a user.
If a PC boots to Safe mode but the problem remains unsolved the problem may be hardware-related. Use the Devicemanager to check if there are any conflicts. Every device needs to be recognised by the operating system and is assigned an interrupt request (IRQ) number. With the large number of devices that can now be added to a computer most Plug and Play devices will happily share an IRQ number but if your computer has non-Plug and Play devices these usually need a specific IRQ number to function properly.