Can You Start a Sentence with "However"?
Although you may have heard otherwise, it's fine to start a sentence with "however." You just need to know when to use a comma because "however" can mean two different things, and if you don't get the comma right, you risk confusing your readers. (来源：英语麦当劳－英语杂志 http://www.EnglishCN.com)
If you use "however" at the beginning of a sentence without a comma, "however" means "in whatever manner" or "to whatever extent."
However hard Anne Hathaway tried, she couldn't liven up a robotic James Franco during the Oscar's.
If you use "however" at the beginning of a sentence with a comma, "however" means "nevertheless"
However, I loved all seven of Anne's Oscar dresses (plus the tuxedo). (来源：专业英语学习网站 http://www.EnglishCN.com)