Turn off the power supply. Unplug power cord. Reset the CMOS jumper (wait 10-20 sec). Plug cord back in. Turn on Power Supply. Now hold down INS, and turn the computer on. You might have to try it a couple times... if still doesn't work try different memory.
Note that this is different than simply holding down INS, or using reset switch because this allows for all the power in Power supply to discharge, and the CMOS of the BIOS to properly discharge as well... that's about as good explanation I can give why it worked for me.
I had the same problem with my OCZ memory and this fixed it...
It happens periodically for no apparent reason, but newer BIOS has fixed this problem (starting from May 2003 I think).
Big question: do you get this FF immediately after you turn the power on, or does it progress from Cx to 1x to 2x etc.. and end up on FF at the end?
The first indicates fatal failure (dead mobo), the later CAN be fixed.