Ok, try this.
Open an admin command prompt.
Type DISKPART and hit enter
Type list disk hit enter
In the list look for the hard drive, probably identify it by size. should be disk 1 or disk 2 maybe.
Type select disk X where X is the disk number then hit enter
Type clean hit enter
You can close the window after this.
Now go back to Disk Management and it should popup saying disk X needs to be initialized. Try MBR again.