Joke appart,

Sounds like a PSU issue to me (but can go wrong)

Can you have it tested with a voltmeter ?

As the LB requires a trickle power of +25V to boot ...maybe this is missing.

this is a useful link:

http://www.xlr8yourmac.com/tips/MDD_ps_mods/MDD_PS_Mods.html

Also, are you sure the CPU is fully seated in the socket.