I am no expert on wubi but your best bet may be to install Ubuntu again. You may want to go for installing Ubuntu alongside Windows 7 it its own sets of partitions.
If you have files under previous Ubuntu installation inside the root.disk, you can copy them to the new /home after mounting the root.disk using these instructions: Can I mount a Wubi .disk image in a new Wubi installation?.
Another approach (This is untested. It may not work and you may lose all the data.) is to:
- make a copy of root.disk and keep it in another location
- Install Ubuntu using wubi again from Windows 7
- Reboot to make sure the new wubi installation works
- Reboot back to windows and replace the new root.disk with the copy of
the old root.disk with existing data
- Reboot and verify the wubi installation works with the old wubi
If the old root.disk does not work under the new wubi installation:
- Reboot to Windows 7, switch back to the new root.disk
- Reboot to Ubuntu, mount the old root.disk and copy the data files to
the new installation.
First, wubi installations are problematic as root.disk files can get corrupted. Second, I have no idea what happens if you copy or move the root.disk files while booted to Windows, in terms of the ability of booting back to Ubuntu under wubi installation. Use extreme caution, if you want to try this. You may lose all the data in the Ubuntu wubi installation.
Hope this helps