My dual screens are flashing, sometimes fading in and out of blue. Sometimes when they flash back to my normal desktop from the blue, everything is frozen, I can't move the mouse or do anything. What is going on with this? I have a Mac Pro Tower, OS X 10.5.4, 2 x 2.8 GHz Quad-Core intel Xeon processing, 6 GB 800MHz DDR2 FB-DIMM RAM. I use this machine to run a recording studio. It is used primarily with a Pro Tools HD3 rig. Please Help