I am not familiar enough with Grub and Grub2 bootloader to help.... I do know there are settings that change the default OS being booted first....
Another option is to try Easy Bcd which is an after market bootloader that is installed from windows. It is quite easy to use and the download and instructions can be found at:
http://neosmart.net/EasyBCD/
this will get you up and running for now...
It does not remove Grub but works with it so you can just uninstall Easy BCD when you figure out the problem you have with Grub....
I just left mine running with Easy BCD because I am lazy....
Oh get the free version on the website if you are only using it for your personal computer...
You only need to buy it if you use it commercially....