disk i/o error

When you get into the CMOS is the date and time wrong?

The disk i/o error may be caused by the cmos not recognizing your hard drive parameters.

The hard drive parameters must be changed.
Check if you cmos has an AUTO mode for the hard drive and set it to that to see if you can boot from the hard disk.

If the date and time are bad, then you need to replace your cmos battery.

And fix all the cmos settings for your computer configuration.

Go into your BIOS (CMOS) and use the auto detect option to find your hard drive (if the option exits).

If the BIOS see the drive then your system is not recognizing a valid set of boot files (msdos.sys, io.sys) or the hard drive is corrupted. If your BIOS recognize the drive then I would recommend trying to recover the Master Boot Record by running fdisk /mbr in DOS. If this still does not work then I would recommend rebuilding the drive from scratch.

If your BIOS do not recognize the drive then start checking hardware; cables, controller, the drive itself etc..

And if neither of the good answers above work, check the HDD cable (swap with a known good cable).
Still not working??
Replace the HDD...