I have a Mac Pro, Dual Core Xeon 2 x 3ghz, running 10.7.5 with a ATI Radeon X1900 XT 512 MB Card with dual monitors of different brands (Samsung & Sony). More than half the time I start my computer, the monitors start off fine and approx 30 seconds later they both go to black and are unable to respond or wake.

I do a hard restart to my computer and then after the reboot, they start working completely fine 100% of the time with no issues what so ever.

Any ideas?