[CentOS] 6.3 installer keeps cycling in a 10 second countdown to boot

Hi.  I've been running CentOS 5 for ages.  (Thanks!)

I went to install 6.3 - I downloaded the 64-bit DVD 1 image, and put
it on a USB drive.  Booted into a screen that said boot will start in
10.. 9... 8.. 7.. 6.. 5.. 4.. 3.. 2.. 1.. 10.. and so on, infinite
loop, the boot never starts.

I tried booting in text mode, but it doesn't boot, just goes back to the menu.

Is there some way to find out why the centos installer refuses to start?

I used to have CentOS 5 on this system.  I'd expect 6 to work.

Thanks,
Aleksey