This is why it is imperative to always have a home backup or an off site backup such as iDrive.
You will want to start off by booting up one of your operating systems first, then connect the 3TB failing disk. If you operating system does not lock up and the disk is detected after refreshing device manager (Windows) Linux should auto detect. Then you can attempt rebuilding the partition table and then recovering your data with Test Disk which you an acquire here along with some how to articles here.
A last ditch effort which can be pricey would be to use a professional data recover service such as Drive Savers.