If one morning you turn on your computer and nothing comes up the most important thing is Don't Panic. Be methodical and follow some logical steps :
If you try to detect the drive in the computer BIOS and it is not detected this is usually a hardware failure.
If the drive is making grinding or loud clicking noises do not keep trying to detect it, you will only cause more damage.
If no noises are heard, start up from a bootable floppy to confirm that the computer works. Connect another good drive to that cable to see if it will be detected.
If it works you now know your drive has failed.
If your Windows drive is detected by your computer BIOS, but you get a message like, "No OS present insert a bootable disk": Try booting from a floppy and then changing to drive C. Do a dir command to try to see the files.
If a message says "Invalid media, abort, retry, fail" hit abort and then try to load Fdisk from your bootable disk.