Clear the BIOS according to the instructions in the manual. Simply removing the battery does not always work.
+1 I assumed he'd done this;
Often there is a jumper you can set when the computer is unplugged; for a duration of 10-20 seconds and then switch it back and start up the computer. IF your motherboard has this; then once done (if done correctly) it will indicate that your settings were reset and it often asked that you go into the BIOS.
IF it does that just say yes, then quit the bios and continue booting the system as every thing will be default.