Why does Pro Tools kill Quicktime?

[TQ1]

I'm a brand new Pro Tools user, as of this week. I have an MBox2 Pro Factory running Pro Tools 7.3.1 and connected via Firewire.

Prior to installing Pro Tools I was able to use Quicktime 7 Pro to watch movie trailers. After installing Pro Tools Quicktime 7 Pro no longer functions even when Pro Tools is not running.

I build my own PC's and my workstation's config is as follows:
Win XP+Service Pack 2
Intel P4 3.4C Northwood CPU(supports Hyperthreading)
Intel D875PBZ motherboard
2 GB of Mushkin High-Performance DDR
Gina24 soundcard (configured as primary I/O audio device)
eVGA 7800GS video card
Three SATA HD's with a total of 850GB of storage
Pro Tools resides on a dedicated partition

I also have Adobe Audition 2.0, Sony Acid Pro 6.0 and Sonar 5 Producer on this workstation. Never had a conflict with Quicktime until I installed Pro Tools.
Can anyone please tell me why this is?

[TQ1]

I got Quicktime to work independently of PT. What was needed was to switch XP's audio output from my Gina24 to the MBox and check the "safe mode" box in the Quicktime player's audio tab.
Odd thing is, though, with this latest version of Quicktime when I import the file into a PT session, PT chokes on the conversion process and hard locks.
Still, I can watch movie trailers again.
I must say the audio quality of the MBox 2 is quite impressive.