can not boot from Western Digital external HD

[cuestakid]

I have a MyBook Pro 500 GB Tripple Interface External HD-for some reason when I hold down option during boot I do not see the drive-I used to always see it but I dont now-I think it has to do with me having to reformatt it a few days ago but I have tried everything to boot from it but no avail-I want to be able to try to boot from a backup that I made to see if it works or not-any ideas??

thanks

 

[CanadaRAM]

After you reformatted the drive, did you reinstall OSX onto it?

 

[cuestakid]

After you reformatted the drive, did you reinstall OSX onto it?

by that do you mean actually installing onto it- if so then the answer is no-so how do i do that-just boot from CD and install from there?

 

[Jiddick ExRex]

You obviously cannot boot from a drive that doesn't have installed an operating system.

Go to Disk Utility --> restore and drag your macintosh HD to the source and the Mybook drive to the destination and click restore. After some time, you have created a bootable OSX image on the mybooks hard drive. It's that easy.