In addition to what @xenoid wrote, you will want to consider backing up the drive before you wipe anything. Just in case you may have any data that you will want to keep. You can do this in GParted, or any modern Live Linux Distro.
GParted is an excellent tool that supports GPT and MBR disks, so grab the gparted-live image, from their website, and burn it to a USB or a CD. I like to use YUMI from pendrivelinux.com which allows me to use multiple distro's on one USB.
When in GParted, select the correct disk in the drop down menu in the top right, then delete the partitions. Select "Apply." You can then right click on the unallocated partition and select "Format", and then create your partition table however you like and format the new partitions to NTFS, or whatever Windows supported File System you want.
Since Windows doesn't see the disk now, you will have to boot to a Linux system like GParted, or even Ubuntu will work if you want to use fdisk or gdisk from the terminal. You can download GParted from an Ubuntu Live boot, but it would be easier to just download GParted itself instead of trying to configure a USB to give you enough space to install software. I suggest GParted because it's easy to use and you should be able to find a tutorial on Youtube if you need a video to see what it looks like. Just be careful and pay attention to what you are deleting, don't want to delete your Windows installation on your main drive!
If you can, take the drive out and connect it to a different computer that you could live boot a Linux image. That way you're only working with one hard drive which would eliminate accidental deletion of data from a different hard drive.
EDIT: I just noticed you said that Windows can see the drive, so if you have determined that you are ready to format the drive, then you can try to format it from that screen from within the right click menu.
However, when you right click on either of the 2 partitions, from disk 2, do you have an option to Change Drive Letters and Paths...?
You may be able to just specify a new drive letter and Windows should then mount the drive.