I get the beachball no matter what...

Here my specs:
HMV 1200 Dual Max, Atto UL4D, G5 Dual with 2 gigs of ram, Decklink SP, F.C.P 5.02, OSX 10.4.2, QT 7.02

I have already updated the firmware of the Atto and HMV, blanked the HMV and re-striped it, yet my problem persists: I get the infinite beachball in FCP when playing a timeline, sooner or later (it takes between 20 minutes to 2 hours to hang). Sometimes it happens in the middle of editing, sometimes during playout to tape. I every case I have to force quit the application (without a chance of saving my work) and then reboot. Sometimes the G5 would not reboot and I'd have to do a cold shutdown.

Just to make sure everything else is okay on the system: When I play media off the internal drives I get neither a beachball nor the spinning pizza of death.

While backing up data I realized that even finder stops responding when copying too many things from the huge at the same time.

Now I hooked up the HMV to a PC via the diagnostic cable to run the disk tests. I just realized that the lower fan was not spinning and gave it a little spin with a screw driver. Now it is working again (I guess I should replace it immediately). Might *THAT* be the cause for my nightmares???

Please let me know

Georg