[Closed] Mac external disk joy

Don't know what's going on here but I'm tearing my hair out.

The Time Machine disk is playing silly buggers - Can see the external device in Disk Utility but can neither mount nor re-format the actual backup partition. I've tried all the usual stuff eg. use of diskutil in Terminal but am completely at a loss.

Anyone have any suggestions? I assume it's got corrupted when the kids have switched the power off without shutting down properly. Not bothered about data loss as I'll just do a full backup (and it's not my only one), but first I'd need to re-format it…