I am using Ubuntu 12.04 along with Windows XP. Nowadays it is working erratically. Sometimes it boots, sometime it won't. Today, I could only login as a guest. I am not able to login as a user.
I think these kind of problems started when I tried to upgrade the system to 12.10. I continued upgrading even though the system cautioned me not to upgrade as there was a graphics hardware problem. Eventually the upgrade failed and now my system misbehaves.
Now, I want to redo the upgrade and fix the graphical problems. I am willing to uninstall Ubuntu 12.04 and re-install. I don't know how to do it without affecting my settings.