Ubuntu – Upgrading Ubuntu from 12.04 to 12.10 broke the system, completely.

First, I hope that this is not a duplicate, because I found my question quite strange and unique, and I don't have any idea with it.
These days I heard of the new Ubuntu release, version 13.10 and I am quite excited. I have been stuck in 12.04 for such a long time and it's time for a good upgrade. So…I ran update-manager -d and tried to go up to 12.10. (I decided to go up one by one)
It took a very long time to download all the required kernel and packages…and soon installing…and some questions asking me if I want to replace the old config files. I did some tweaking with that system before (changing startup applications, TMPFS, zram-enabler, etc) and I thought that it will cause a real crash if I keep these config files. So, I replaced all of them but it goes too slow and it's time I've to go to school. I asked my grandfather if he could help me to click all the 'Replace' buttons for me and shut down the computer after the upgrade finished.
When I was back from school, he told me that he accidentally clicked 'Keep' for the last popup box, and my computer can't function now. The grub menu is still there (made it appear by using the SHIFT key trick), and the splash screen is still visible, and I hope that the login screen is still there, or at least the tty so that I can still do a rescue, but nothing worked. CTRL+ALT+F1 does nothing, and I am sure that the monitor is still functioning.
So what can I do now?