Xwindows locking up on boot

[Randolph Jones]

I have FC3 2.6.11.7. I have been ok for some time, and recently
my system fails on boot every other boot
the x window starts and fails at hardware check, requiring
poweroff and restart
next boot is ok, but if I use cmdline shutdown or the menu it will 
freeze the next boot
the mouse moves but keyboard does not respond
the display freezes during the hardware check
I dont see anything in the messages file
Any ideas where to look for the problem?
TIA
rfjones