I have a E420R with 4x 450Mhz CPUs. In an effort to conserve power and
air conditioning in my computer room, I decided to yank two of the
CPUs.

According to the manual, running a E420R with two CPUs is fine, but you
have to remove CPUs 0 and 3, which I did, leaving the two middle CPU
modules. Upon rebooting the server, I get a blank white screen. No logo
in the upper left. Nothing. I thought maybe there was some kind of
jumpers or something I might have missed, but there is no mention of
anything of the sort in the manual. It does recommend putting blank
placeholders in the empty CPU slots and I don't have any of these,
however it's hard for me to imagine that they do anything.

Any thoughts?

What's worse is that putting the two removed CPUs back and restarting
results in OpenBoot starting up normally, and then freezing after the
memory scan. This computer worked fine prior to this!!