iPod will not interact with itunes

I have very carefully installed a new logic board, battery and screen in my IPod 5th gen video.

When I switch on the unit, after a slight delay the screen lights up but is otherwise blank. I can hear the disk start up and after a while switch off.

The unit is not recognized by ITunes. The icon doesn't appear in ITunes and no apple logo appears on the IPod's screen.

This tells me that the battery is working as is the hard drive and screen.

I understand that the Operating System is installed on the hard drive ( which is original and was working correctly before I started the upgrade).

My question is :- Does the unit need to be flashed with the OS and if so how to do this.

Thank you,

Keith Rhodes.