After years of trouble free operation, my pals eMac freezes, forcing me to use the power-off button to restart. When it locks-up, very often the screen presents a highly jagged image (the scan raster appears to be out of sync at this point) and nothing is legible or operable. Even the cursor is locked in position. The fault can occur at the blue stage of booting or much later when opening or attempting to use one of the applications.
I've clean-installed the Mac OSX (10.4.11) op system without any additional software or re-installation of clients files.
No USB or FireWire accessories (apart from the keyboard & mouse) are refitted. I've tried using my own eMac trusty keyboard and mouse too without discernible difference.
I've run TechToolPro4's advanced test regime, repeatedly and no errors are found.
What do I do next please?