How do you reformat a hard drive?

How to reformat a computer hard drive?

format c: at the command line prompt...however, if you're using the computer, don't do it, as that will erase your data.

Modern disk drives no longer require a low-level format.

The formating that thedude is talking about is just putting a filesystem on a partition.

Anyway, why are you formatting? If you are getting disk errors than your disk is probably going to fail soon. Back it up while you can and buy a new disk; disks are cheap enough now that it isn't worth it to keep data on a dodgy drive. If you want to format to scrub data off the disk the format program is not adequate because it just blows away the VTOC and leaves most of the data intact for anyone motivated enough to manually piece the data back togethert. If you want to wipe the disk clean look into a utility called DBAN, it is free but does a very secure job of erasiing data..