Ubuntu – Repair ext3 partition on external disk from Ubuntu 10.10

generally the concept is to mount the filesystem read only (that's why a live cd is needed). for your case, since you have nothing you could start the system in single mode (add 1 in your boot parameters).

Another thing you could do is to make a usb bootable (unetbootin) and boot it (some idea as live cd)

You could also you another disk for temporal boot and just mount read only your actual disk.

And many many other things i cannot think this moment. But as i said before, just find a way to mount it as read only.

sudo chown Username /media/usbdisk

I would also add a -R so it operates on all files and directories.