|"I have a used Lenovo ThinkCentre desktop from a company that went out of business" Best bet is to ask them for the code.|
I have repaired and do maintenance on a number of PC's from a medical company and they use the same sign in as you described.
In my experience, unless you know the log-in you cannot even get in to safe mode or for that fact also cannot change bios settings to boot from CD first. It is an anti-theft feature.
You can try popping in a different hard drive and see if you can load up an operating system, but I think you may be dead in the water. Good luck.
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