A good start is probably to reset the CMOS on your computer. This will restore the configuration options stored by the computer to their factory defaults. Do this by holding down the Delete key on the keyboard while you switch the computer on. (If you'd like a more detailed description of the whole malarky, have a look here.) Note that you must actually use the power switch! Using the reset button isn't enough.
Once you've reached the desktop following this, press the F12 key and type:
Configure IDEDiscs 1 and press Return
Configure ADFSBuffers 0 and press Return
Configure FileSystem ADFS and press Return
Configure Drive 4 and press Return
Configure Boot and press Return
ADFS and press Return
Opt 4,2 and press Return
Finally, press Return again and then re-start the computer.