Hi there, my name is George and I am a business analyst by trade.
I have had an issue like this before myself and managed to resolve it.
I am an expert in Excel VBA and I use social networking sites.
It depends on what browser you are using, there are steps you can take to get it to log in, it could be many different things and it's usually related to the last changes you made on the computer.
I would be happy to work through this issue with you and advise on the steps to take.
Kind regards
George