Applications crash

by MarTayNy - 1/3/12 3:36 AM

MacPro, Quad Core Intel, 3GHz, 4 GB RAM, OS 10.5.8
Working as a graphic artist, I most often use Adobe Photoshop as well as InDesign, and rarely Illustrator, etc. (CS 5). Sometimes I can work for hours, no problem and then applications freeze inexplicably, abruptly. They will not force quit and I cannot restart from the menu bar, and must turn off the power button and back on. I've zapped the PRAM and repaired permissions countless times, and removed all of my many fonts and carefully reloaded them one by one on an as-need basis. I've taken this computer to the Apple Genius Bar 4 times in the last several months, they've run a number of diagnostics and replaced a couple of minor pieces of hardware and say everything should be fine. But still the applications crash (Mail, Photoshop, you name it) and now job files that were saved sometimes become corrupted when I go to reopen them.

Any ideas as to how I can find out WHAT is wrong?