VHS to digital, flickering, lack of video and good sound
If you are using old VHS player, then its head can be dirty

Also VHS cassettes' tape can be dirty, but how I understand you using new cassettes. 

So, try to connect your VHS player to TV. If signal will be the same, you need to locate that thing:

And clean it and head (black thing on background to the left)

You can do it by yourself or maybe there still exist place in the world, where professionals can do it for you.