Hi Daz,
When you say lower drive board I presume you mean the SD board?
The best way is to disconnect the SD board completely from the set (you can leave the screen ribbons connected, but make sure nothing else is touching) Then switch on, if the SD board is faulty then you will just get the Top half of the screen working, if the set doesnt work then the SC board could be faulty.
The problem is that a defective screen can 'blow' your Sd board, and you won't know if the screen is faulty until you fit a new Sd board.
You say the picture had lines, can you post a pic? Normally when SD board blows the set becomes dead
Regards
Brian