I/O errors usually (but not always) indicate failing hardware. My guess is that your disk (or some other disk-related component, like a cable or your motherboard's disk controller circuitry) was on its last legs, and the "exercise" involved in installing Ubuntu caused it to fail. You don't say what prompted you to install Ubuntu, but if you were having problems with Windows reliability, it's possible that this was an earlier symptom of the problem.
You might try unplugging your disk (from both ends of the cable if it's a desktop system) and plugging it back in again. You could also try running a SMART test from an Ubuntu live CD -- but if the disk isn't detected by your firmware, it might not even show up in Ubuntu, which would make such a test impossible.
If you've got a spare disk, you could try using it instead. If it works, then you can pretty much conclude that your old disk is dead. If the replacement disk fails, too, then chances are the problem is with your computer motherboard's circuitry.