Reset bios password of Lenovo fails (asks for password and PIM)

I’ve got an used Thinkpad which asks for a password. Since the password prompt is a black screen with just the letters Password: in white I assume it’s a BIOS password. To remove it I followed instructions such as these. I opened the laptop, removed the battery and the CMOS battery, and after a couple minutes I reconnected them. After doing this I boot it up. It makes a short beep and then very shortly flashes on the screen:

0251: System CMOS CHecksum bad – Default configuration used.

And after that it proceeds to the same screen as before, which asks for the password. If I simply leave it blank and hit enter it then asks for a PIM. I leave that empty as well, but as you can see below it refuses access.

Does anybody know what I can do to remove/bypass the password prompt? I don’t care about the data on the laptop (I will probably flash it and install some Linux distro on it).

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