I had the exact same problem and just wanted to write how I fixed it for anybody else trying to find a solution.
There is a cable that goes between the computer and the screen, seen in step number 9 in this guide: [guide|8985]
Do everything in that guide until and including step 5. When you have the lower case removed, turn the computer on. Now lift the plastic tab on the cable shown in step 9, but do not unplug the cable. This made the display return to normal for me and also stopped a high pitched noise coming from the connection.