I had the same problem and the fix was easy.
1. On the windows icon at the bottom left-hand corner, right click.
2. Select Computer management option from menu.
3. Under the Storage menu select Disk Management.
4. On the right there will be a list of drives under Volume.
5. Select the SanDisk drive and you will see there that it will have two paritions.
6. Before proceeding to Step 7, make sure that all information on drive has been backup or saved on another drive
7. Right click on the partitions and delete them. It will likely say 119.25 GB unallocated after you delete them.
8. Now you can format the entire drive as one. Right click and select New Simple Volucme…
9. A wizard menu will appear follow the instructions. I simply select next to everything and finish.
10. When done the drive will pop up, close it. And in the Computer Management you will find the assigned drive.
11. It shoud say "Healthy (Primary Partition). It’s ready to be used.
I hope this helps…