IBM Thinkpad t40 power on password problem

Hello!
My uncle has a problem with his laptop which is an IBM Thinkpad T40 2374 CG5 model. His son had used it for a time, but he died before some years, and now my uncle found his laptop and wants to use it for his needs. But he does not know which password his son used to use. He gave me some suggestions, but noone seems to be the right one.
I read that there are 3 types of passwords that can be used in an IBM Thinkpad notebook, and this one seems to be a power on password together with a supervisor password, because the operating system won`t boot and I can`t enter bios either.
I removed the backup battery (as it was shown in the manual of the laptop), then powered on the laptop (after 20 min) but the password was still required. The only thing that went different is that before displaying the request for entering the password, the screen displayed 3 types of errors indicating (1) to put the date and time, (2) System CMOS checksum bad - Default configuration used and (3) Keyboard error. Then I replaced the backup battery again, but still the problem persists and this error messages are still shown. The password was not reset.
Does anyone have any other sugestion pls?!

 

http://www.tech-faq.com/reset-bios-password.shtml
or
http://sodoityourself.com/hacking-ibm-thinkpad-bios-password/