Grayish/Blackish screen. Iphone not responding. What do I do to fix it? Help!

So this morning I woke up to check the weather on my iphone but nothing came on but a grayish/blackish screen. A window pops up saying "Itunes has detected an iphone in recovery mode. You must restore this iphone before it can be used with itunes." I click ok and the restore iphone. Everything appears to be going ok, but then in the progression panel it says verifying iphone for restore. Then a window pops up saying "The iphone could not be restored. An unknown error occured (40)." I have tried multiple times to restore it with itunes like the apple support page has said, and have even followed the rest of the troubleshooting directions. What caused this, why won't itunes restore the iphone, and how do I ultimately fix this problem?