HP EliteBook 840 G1 - BIOS reset and now it needs Administrator password

[FaneDuru_FG]

Hello,

I have an EliteBook 840 G1 which started to not keep the current time. I suspected the BIOS battery and I ordered a new one. Until it came I tried seeing where the battery is trying to prepare a rapid replacement. I disconnected it from the board and could see it was stack with some double adhesive tape. I placed it back but starting from that moment I received a "CMOS Checksum Error". I read on the net that it may appear when BIOS battery is disconnected for a little longer time. So, I waited for the ordered new battery to come and now replaced the old one. 

I do not receive the CMOS Checksum related error but now, trying to enter BIOS settings I need an Administrator password, which did not exist before. I suppose that BIOS has been reset to the factory settings and I also suppose that there must be a default such password for every HP notebook model. Maybe, i am wrong...

So, can you supply such a default password?

If my supposition is wrong, what can I do to enter BIOS settings? The 'new' BIOS does not see the installed OS. It probably is set on some legacy way of BOOT, or something else. 

I can see (after Escape pressing) an option of "HP SpareKey", which I do not remember about.. Would such a key solve the case? If so, where from to take it and how to input when necessary? Choosing this option  (pressing F7) followed by pressing"Bios Administrator", the single option, it returns "HP SpareKey Recovery not enrolled"...

I tried entering three times a wrong password to receive a specific numeric code, but nothing has been returned.

I tried reinstalling the OP but BIOS does not see any USB...

Please, help me to solve the notebook problem.

Thanks in advance!