How do you get booting to stop to troubleshoot?

This computer on the network is also acting up. See other post. This computer continues to boot up and whether I try to pick Start Normally or any of the safe modes it continues to cycle through and never stop. At some point before the big windows XP pops up on the screen, a screen with a blue background and some writing pops up, but it is so quick, you can't make out a single word or hit whatever key it is to stop it there. So I obviously cannot get any further to troubleshoot this computer, I can only imagine what I'm going to find.