Hello, i need help fast!!

[AC Question]

Hello! I have a desire 300. I have a problem. I used it few months ago, then it was all good all worked, today i took it out again from box and saw that grey thing aronund display, can someone tell me what is this? is my display broken?? when i turn mobile in then display is not working, last time i used it worked fine. Please help.. Picture here imgur.com/a/xjcNE