Display shuts off when vista boots

I'm having a problem with my display shutting off when I boot Vista.
The monitor turns on when I turn on my computer. It stays on through the
progress bar. But once that part is done the monitor will show a "No Signal"
message and fall asleep.

Now, this only happens in certain circumstances! It only happens if say I
have my external Hard Drive attached, or my iPod is plugged in. Sometime's
even if there is a CD in the drive. This will also happen if I restart the
computer from windows.

As long as no extra drives are attached and I do a fresh power up 99% of the
time everything will work.

I'll hear the startup sound and the hard drive LED will be flickering. I can
leave it on all day and the monitor never wakes up. So I'll hit the PC power
button and you can tell Windows will shut down properly because it takes the
regular length of time to shut off as normal (I think you'll even hear the
shutdown sound, can't remember) - you just can't see it happen.

I've tried reinstalling the drivers and even using the on board display.

Any ideas or suggestions? Thanks! (VisionTek Radeon X1050 is my video card)