My colleague has linux and ubuntu already installed on his machine, but can't seem to get access to it. The drive seems to be running, just can't read it

Have tried it on a colleagues computer running Linux, but he isn't getting much joy. Any other advice?

I've downloaded Linux Mint but not sure how to now install it on a USB stick and then boot up my machine with it.

Never used anything but Windows

My external hard drive is showing an error.

G:\ is not accessible.

The disk structure is corrupted and unreadable.

Does anyone know how to fix it without formatting it? Have a lot of file on...