Thank you for the tip
Well.. there's a part in this guide where it says:
"Ubuntu cannot be booted if Windows has not been shut down cleanly, you have to clear the Windows filesystem from Windows (there is no chkdsk equivalent for Linux yet). If Wubi fails to start, boot into Windows, run chkdsk /r from Windows on the same drive where you installed Ubuntu, shutdown cleanly and then try to boot into Ubuntu again. "
That's true. In fact, my Windows (7) doesn't "shutdown cleanly" because it has a problem that I never find a fix, where it doesn't shutdown. The system keeps in the "Logging off" screen, so I have to long press power.
But I ran the chkdsk and it still doesn't work!
I still can't boot ubuntu, can't even use that grub command line.
And the folders listed in the Guide (C:\ubuntu\disks\root.disk and C:\ubuntu\disks\boot) are there.
Any other suggestions?