If you're doing your format outside of your drive (as in, you aren't reformatting the OS disk while in the OS) and you're getting stalls and instability, your drive may simply be failing.
Try running the drive check utility from within the OS by right clicking the problematic hard disk -> properties. Or run a chkdsk from command prompt
(Assuming you're on Windows), If you can still access your OS.
Is it stalling anywhere specific?