Hey I dont know if you fixed your problem or not, but for others I wanted to respond. I had the same problem with my 600m and the problem could be the actual hinge being broken in half, mine was and not from damage, but just wear and tear from very easy use. The thing would be simple to replace. CAREFULLY pry off the plastic hinge cover from the right then over slowly to the left. ( I just replaced a keyboard in an E1505 Inspiron. ) Anyway..there is a metal hinge behind that. Two screws out, new hinge on, be sure it is straight, screw down the new screws and voila, no more separation. CAREFULLY put the plastic hinge cover back. Probably be able to get those hinges on ebay..
hope it helps
I'm having a problem with the hinge seperating the cover and the lcd screen. I did what you suggested about how to get into it and unscrew the screw. The problem I have now is how do I get the hinge out once the screw is out, and without breaking the screen or cover? Can you please help me?