locked Board no upload, no reset, only ON led and L led

Hello,

everything was working well with my board; then I wanted to use it and couldn't do anything
programme doesn't work
cannont opload
can't see the board in the device manager
can't reset it: L led doesn't blink
Only PWR and L led are continuously on

I tried with different cables, and 2 computers (XP and Linux)
my board is a leonardo

IDE says:

Connecting to programmer: .avrdude: Send: . [1b] 
avrdude: Send: S [53] 
avrdude: ser_recv(): programmer is not responding
avrdude: butterfly_recv(): programmer is not responding

as if nothing was programmed...
4.87V on the board

please help me, I use the board as a car engine managment! so I can't drive anymore
here is the project:
http://forum.histomobile.com/viewtopic.php?f=33&t=1259&sid=e3355d5b972d71153435d8c44736cee6

thank you!