Unable to select .ISO file in Startup Disk Creator

I am trying to create a bootable thumb drive w/ a Windows .ISO I have however Startup Disk Creator doesn't allow me to select the image.

When I open Startup Disk Creator I see the box for "Disk to use" which is my USB and a box for "Source disc image (.iso)". Now when I click the "Other" and select my .ISO fiel then click open it the window disappears and nothing happens.

I am running 18.04.

Startup Disk Creator is not a general purpose ISO burner. It is best used to make an install media of the current running Ubuntu system. On some Ubuntu releases, Startup Disk Creator will even fail to make a disk with an ISO of the next release. In some cases it will actually write an unbootable media, mixing inconsistent bits and pieces from the ISO and running system.

Lowest level is to use dd to copy the ISO directly to the media, but a tool like mkusb might be better, to provide some sanity checking on where you are writing to. The right click mentioned in another answer should work too.

You could try right-clicking the ISO then OPEN WITH >> DISK IMAGE WRITER >>and then select the hard drive or disk and enter your root password