bios is the settings that control your board (harddrive processor, graphics)
if you are using a dell i think you need to be hitting f12 right at the start.
you don't want to really touch anything in there but just look around and see what the settings are at.

but yeah it cant hurt to have it checked if you can figure it out yourself

goddamn it just remembered you can set the boot options using the properties on the my computer right click

right click on my computer select properties hit the advanced tap then in the starup and recovery section hit settings the first option to change is default operating system its a drop down menu if there is more then one windows os on there it will be listed. (i cant believe i didn't think of this sooner.... for a at school we were running boxes with two OS's and had to switch constantly )

so see what the shows you