Mac Pro hangs at startup showing white screen with spinning pie wheel MacPro 1,1; lion?

startup hard drive failed (with loud buzzing).  Removed bad drive, installed replacement, inserted Lion USB drive, verified new drive using the Lion usb drive, started installation of lion on new hd, message on screen advised that it would take some time to accomplish, but after installation would shut down and restart. So I left the room to return a few hours later to a white screen w/ spinning pie wheel.  

Repeated startup attempts (with or without lion usb drive inserted) proceed as follows:  startup chime, gray screen, gray screen with apple, gray screen, white screen with spinning pie wheel, all in the first minute then nothing further. 

Since the lion usb drive is apparently no longer being recognized I thought I would try to do a startup with a mountain lion disk but I don't know how to insert the disk with the machine hung in startup. By the way, the system that was installed on the failed drive was mountain lion, not lion, if that makes any difference.  Time machine resides on external hard drive and will be connected and used to restore once machine can boot.
Turn off the machine, than boot again and hold the option-key ("alt" on some keyboard layouts) right after pressing the power button. A menu should appear where you can select the device to boot. Perhaps try formatting the drive and reinstalling again.