Strange, I have a 4400 and it should not have caused it to do that. As David already said, it would have cleared the BIOS, but the default settings should have booted and should not have affected DHCP settings either (that is set in the OS, not the BIOS).
Look for it on the LAN with Snap Manager, or check your router (or device used for DHCP) and see what IP it is being assigned. Also as David said, the default is 10.10.10.10 if it does not get an IP assigned.
The COM port settings David mentioned are set in BIOS.
Of course, with no video, all this BIOS stuff is not going to be just a 1,2,3 type deal.
Note for David: The 4400 does not have a Video, PS2 Keyboard, or PS2 Mouse port. It only has the GB ports and USB ports. This makes problems much more difficult to solve (but not impossible). Maybe another unit for me to play with?