since no one else replied. Couple things possible.
You have a powerful 3.4 computer with a powerful X700 PCI Express card, and along with other drives/accessories, it seems like a strain on your power. Did you put in a high power wattage unit from a good name company when you built? Even 450W on a cheap power supply can register much lower...see Tomshardware.
Another is ATI drivers which seem to have problems.
Also the monitor and or card may need settings to around 75-80 Hz.
I just built a system using 775 chipset w/ a D915PBL Intel motherboard w/ 3.4 processor and installed a PCI graphics card ATI X700 and after its been on for awhile the monitor turns on and off until it speeds up to fast to read screen have to reboot to fix problem it seemed to do it more when I plugged in a front usb device and had a couple of prcesses going on this is the second X700 I had the other one did it so often it was totaly useless this one is better and yes I did install the new Catalyst 5.2 any others with like problem very frustrating and answers would be extremely helpful. the first one I did a disk clean from windows xp and that started the problem like now reinstalled and picked up other card which hasn't been as much of a problem but I want a rock solid system and now I'm constantly worried that am going to loose monitor viewing, and yes I checked monitor on laptop and know problems at all, sorry if this is long winded. Clint