Xbox 360 Error 66 problem

i bought an Xbox 360 off some guy who was trying to soft mod it but his pc crashed while he was flashign the drive.
I could never get it to be seen in windows using the Team xecuter connetion kit so i sent it off to some company and they had to replace the logic board on the drive and put the original key back on it.

Now when i put the drive back in and reassemble the xbox it comes up with E66 and has the bottom right led as red.

i have read up that the firmware is the problem but can't find anywhere that tells me where to fix it.

Can anyone help please?!?