@ USAFRet: LOL.
@Emmannel_: We're not trying to bankrupt you, mate, just help, we've both made this mistake and want to be sure you don't follow us down the same hair tearing, head banging, fury inciting road.
Find some way to backup the files, either to USB stick/s or DVD discs, or a free Cloud storage place like Dropbox of One Drive.
Failing that rename each drive: Start>My computer>right click on 'drive letter' in the box that opens click 'properties' and there should be a box for the Volume Label, change this to something useful, then 'Accept', rinse and repeat for the other drive.
By renaming each drive this way it'll be much easier to see which one you will format and install to later on.
ONLY format and Install to the named 'C' drive, do NOT take any notice of any other entries in the HDD list generated by Windows during the install, including unallocated space and system reserved space, JUST the 'C' drive (or whatever you name it).