I found a Surface Pro that something is selling but without the screen assembly.. I can only find the Surface RT screens...

From my experience, the metal plate at the top of the screen is put back on, it never works again once its removed from the screen. If thats on there, then thats your problem, if its not, then its just the poor adhesive they use. Ive had this problem in my store when I fix ipods. I found out the solution is to take super glue and put a DAB on each corner and put small clamps on the corners to hold it down. If theres pressure on the LCD, thats probably because they didn't secure the metal plate underneath all the way down.

You might have it unplugged or might have cracked it while putting back together. Hold the power button and home button at the same time for 10 seconds until it shuts off, and try to turn it back on. If that doesnt work, check the LCD connector. If thats not it, you probably cracked it putting it back together.

There needs to be a UV film in there in the square to the right over the ear piece. It something sticks to the glass when you take it off or falls out. Also, if you have a different color screen, that also might be the issue. As I am a phone technicians.. Ive worked on thousands of these iphones. This link should solve your problem - http://www.ebay.com/itm/iPhone-4-Proximity-Sensor-UV-Sticker-with-Foam-/221162423537?pt=UK_Replacement_Parts_To... If it doesn't it might be the screen or might even be the power flex. Or even both.