System freeze....

I had done a couple of reboots yesterday to install a couple of USB devices
and then needed to uninstall a printer and then reinstall it. I did another
reboot and my XP Pro system with an Intel Dual core 2.4 Ghz machine only
displays the first DOS screen, the one with the F button functions at the
bottom of the screen. No matter which F buttons I try, it will not show me a
boot screen or anything else. I just sits there and is frozen. I even tried
rebooting with my XP CD in the drive and it wouldn't recognize or react to
that either.

What could have gone wrong? More importantly what other emergency boto
methods are available?