[X4U] G5 1.6 GHz no video

[Spoolman Nancy]

We had a G5 Tower 1.6 GHz computer sporadically lose it's firewire.  
We ordered a new logic board and put in the new one. Now the video  
will not come on. We get nothing but a black screen. Has anyone else  
had an issue like this? We went to the Apple Discussions and so far  
one person asked a similar question, but no one answered.

Thanks for any information you can give me.

Nanc