Mac Pro hangs when booting alternate partition

I'm having two new problems with my Mac Pro (3 Ghz, 4-core).

1) I have on one of the drives a separate OS X partition to boot from (10.4.11). It hangs just as it gets to the desktop and goes no further. I never get a menu bar or a pointer or any of my desktop icons. The booting never finishes. I've tried to re-install the OS, except for problem number 2.

2) When I try to boot from my Mac Pro CD ROM, it does the same thing. It gets to the blue desktop and stops there. No pointer, menu bar, or anything. So I can never get to fix problem number 1.

My main bootable drive in bay 1 still boots just fine, although it frequently seems to take a tad longer. But it does finish the booting process so I have a partition to work with.

I recently replaced the stock cooler on my X1900 graphics card, and that's when the problems started, though I'm not clear how that could be the cause.

 

Solved.

The setup included a second monitor, but I rarely actually have the second one on, so I didn't consider it as part of the problem. The pointer and menu bar were over there.