Key Product not being requignized for Office Product Standard Trial

I’m having a laptop with Windows Vista running Office Standard 2007 trial version. I bought a product key for the same to activate it. But the problem is now whenever I put the keys to activate, it gives me an error Invalid product key.

Can anyone advice me what should i do ?

You can also activate the same by using an call service. There is an automatics voice system which can let you to activate your product by phone. Normally, to install Office you must have an clean installed operating system. Have you ever tried to activate by calling the toll free number 0800 2848283. So at least after you with a call center employees of Microsoft will personally connected. Which you explain briefly the situation, then you will be given an unlock code.