bro0..just reintall wordpress and then use your backup....i think it should work for you now...there might problem eith your wordpress ......
Yeah install a fresh wordpress with a default theme and then do the full restore. If this won't work then the back up which you have downloaded might have been corrupted.
Then the only solution would be left is to contact your own hosting provider for a last backup. If they tell you that they don't have any backup then its a big lie.