Startup display problem

I have an ATI 9600 on windows xp pro which has worked perfectly for two months. Now on startup POST displays then at the 'windows loading'screen the bar is blocky and lined and colors mixed up, when startup is completed I have a black screen. If i then boot to safe mode, neither 'last Good Config' or 'VGA' is any different. Safe mode gives a screen with it all blocky and lined, but I can see behind the lines and colors to go to System Restore. I can even clear the lines and blocks to clean the Safe Mode screen by waving the cursor over the page. System restore works perfectly and the display is okay thereafter.(I can even Restart with no problem)..until the next cold boot. I have checked connections, new cable etc. Any help would be appreciated.