As long as the Hamburger meat has been properly frozen then brown hamburger meat doesn't always mean it's bad or unsafe to eat.
Naturally overtime hamburger meat can turn brown or even gray in color but it can still be safe to eat as long as you've kept it frozen to prevent bacteria from growing.
I've eaten and cooked hamburger that has turned brown and even gray before and although it didn't taste as fresh the hamburger was still very safe to eat.
If the hamburger is bad it will likely have a bad foul smell to it that would make you want to vomit but as long as the hamburger meat still smells good then it's likely safe to eat.