There isn't anything already installed that can access the disk. This tool can be used from Windows to get readonly access to the
\ubuntu\disks\root.disk but you may have issues if there is file system corruption.
You should boot from an Ubuntu CD/USB in live mode (select "Try Ubuntu") and fsck the root.disk as described here. For example, if your root.disk is on /dev/sda1 you would (change /dev/sda1 as appropriate):
- Boot a live CD/USB
Mount the Windows partition
sudo mkdir /media/win
sudo mount /dev/sda1 /media/win
Fsck the root.disk
sudo fsck /media/win/ubuntu/disks/root.disk
Don't fsck the root.disk if it's mounted.
PS for Wubi it's important not to do hard resets. See here.