I am almost certain I know what my problem is, however I'll relate the story as it may help someone else.
Duncan suggested doing a big emerge while in an xterm. Only HAL & Gentoo sources 2.6.27-r8 where available as upgrades which I did. I then rebuild xorg-server, libx11, & glibc. I was getting sure that it would not hang, as rendering text isn't much of a load, however during the glibc compiles it did hang. When I tried to reboot, nothing showed on the screen. I've had this problem before, always heat related (hot days), however it was not a hot day, so I suspected dust. I opened up the case to clean it & found the case fan was very dusty, almost blocked. Everything else didn't look to bad. However I took the CPU fan off & found that while the fan wasn't too bad, the heat sink itself was chocked with dust. After cleaning & reassembling I found that the case fan was back to front (sucking air INTO the box) & has been like that since I built the computer, so that hasn't been helping. I also noticed the graphics card fan would try to start but soon stop. I took the card out, dismantled the fan & also found its heat sink very dusty. After cleaning & reassembling it was still dead. My theory is that the graphics card fan has been starting, but running at low efficiency due to dust. Once the graphics CPU is exercised enough to heat it up beyond the fans ability to cool, it would shutdown/lockup, hanging X. In retrospect I should have investigated the 'blank screen on hot days' problem more deeply, then I might not have had this problem. I'm currently using the mother board graphics, have 2 firefox sessions under X for more than 2 hours, with no problems. On the bright side, my card hasn't been sufficient to do all my graphics requirements & I've been thinking of upgrading for a while.
