Your Celeron 600 is probably cc0 stepping (default voltage = 1.7v).  Intel changed the reset pin location on the cc0 Celerons.  You can fix this problem by adding a jumper from cpu pin locations AH4 to X4.  I did this mod on my BM6 by soldering a jumper on the back of the motherboard.  My cc0 566 wouldn't post prior to adding the jumper and is now running stable at 936 MHz.