Trouble upgrading 10.4 to 10.6

[iabdllc]

I had to do a clean install to factory settings on my husbands MBP. I have time machine backups stored. I used the original install discs that came with it and that went well. Then I went to upgrade to Snow Leopard and it all fell apart. Upon what seemed like completion of the install I got a message that the disc I was installing it on could not be changed and the install failed. Since then I can no longer get the computer to go beyond the gray screen and apple, then screen goes black. I've tried restarting with original install disc and also holding option key to choose hubbie's HD as start up but in all cases I end up with a black/dead screen. What have I done? did I ruin his computer?