The other night I began receiving warnings of immenent hard disk failure, so I backed up my computer to an external hard drive. It seems my boot disk was also backed up there, so if I start up my laptop it gives me a boot disk failure message unless I have my external hard drive plugged in, in which case the error does not appear, but instead the screen stops at a blank command prompt. I know I have to get the boot disk back on my computer, my question is how do I do so since I cannot start it up to properly to restore the files I backed up?
Please take the following educated guesses with a grain of salt. I may be wrong.
A backup won't move / disable your boot drive. It seems more likely to me that you manages to image the drive to the external drive, and then the boot drive died. BTW, what software did you use to make the backup, and is it an image backup or a clone? Was the external drive bootable before?
You can test the failed internal drive assumption by one or more of the following methods
Remove the external drive. Boot to BIOS and see if the internal drive is detected. If it is, try to boot to it.
Remove the external drive. Boot to a drive utility if you own a bootable drive utility, and examine the internal drive. If it's dead, then it's dead.
Boot to the external drive, bring up the Disk Manager, and examine the internal drive to see if it is detected or dead.
If you can see the internal drive, you can try a repair install of Windows.
Congratulations on getting a backup done in time. If the internal drive has failed, instead of some transient file corruption, you will have to buy a new one, replace the dead one, and then copy your saved image back to the internal drive. My guess is that this is the most likely scenario.