I got the dreaded 00 a few times after sudden power outages which can corrupt many mobo settings.
A hard reset can only be ensured reseating the battery. Hold down the case power and reset buttons for a few seconds while the battery is out. This grounds the mobo which ensures any residual power to pins is cleared.
Soft clearing functions and fancy CMOS buttons don't always completely clear ALL settings. The battery is used to persist some chipset settings. Eg. SuperIO settings may not clear unless ALL power to the system is removed.