I have microsoft office 2010 starter on my laptop which i bought June 2011. I wanted to use my existing version of 2007 and installed and used it successfully since then. However, this week, and I haven't done anything, my laptop has started opening existing documents in 2010 version, and in the case of excel files isn't giving me the option to right click and open with 2007 excel version. How do I change my default setting back to the 2007 program? I assume this is what's needed. (I'm not technically computer minded). I can't even find the 2007 version in my programs!

please help someone. AND THANK YOU!!
Nikki