Upgrade to Celeron 2.8GHz Doesn’t Work

I have a system based on a Chyang Fun CFI-S969L motherboard. It was a self-build and I originally built it with a Celeron 1.8GHz CPU and it worked fine.
I recently decided to try to upgrade and bought a Celeron 2.8GHz CPU. The docs with the new CPU say it works on 533MHz FSB. The manual for the motherboard says it suports both 400 & 533 MHz. The BIOS has a setting to detect this and it’s set to autoselect (it also set the memory speed and I have 266MHz memory, which is in the supported range for both the slower CPU on 400MHz FSB and the faster 533MHz FSB.
So on paper it looks like it should work, but when I plug it in it doesn’t. I don’t get anything – blank screen, continous fan noise, no activity from hard drives.
Any suggestions?