'''Have you visited this page''' at [http://support.apple.com/kb/ta26930|Apple]? Or this [http://manuals.info.apple.com/MANUALS/0/MA321/en_US/Using_Xserve_Remote_Diagnostics.pdf|PDF manual]? Also [http://support.apple.com/kb/HT2652|which LED's are lit] makes a difference.
'''On the non-booting machine''' try a [http://support.apple.com/kb/TA27193|PMU reset.] As for starting with out a CPU - I would think that the EFI is killing that machine as it fails POST (Power On Self Test).
''If this answer is acceptable '''please remember to return and mark it'''.''