You can try to load BIOS defaults and press F10 key to 'Save and Exit'. Once done, change the settings.
Here is the video and the Owner's Manual for your reference.
Hope this helps.
Thanks and Regards,
I've replaced the CMOS battery on my Dell Inspiron 531 and the system date and time now show as correct, however on boot up it still goes to the error screen with 'CMOS battery failed' message and request to click F1 to boot or F2 for system set-up. In the manual for the 531 it tells you to go to the 'Maintenance Section' in the system setup and clear the errors in the 'Event Log'. There is no 'Maintenence Section' and hence no 'Event Log'. Any ideas on how I access and clear the errors so my machine boots up cleanly?