But this happened twice. The first time it was the usual things plugged into the USB ports. Fix? Unplug everything, try again,.

The second time it was the old "trip up the install by formatting the drive ahead of time" issue. Fix? We removed all the drive partitions and let 7 partition the drive and install.

Hope this helps.

Now there is some talk about an old BIOS that caused this but I haven't seen that.
Bob