You could plug in some USB fan, light, … and see if there’s power on there. Maybe prepare a harddisk on another computer, boot Linux and look at the debug logs. See if the USB chip gets recognized. And maybe learn something about the topology… If it’s just a single controller or multiple ones in there.

First thing I’d do is reset the BIOS. Maybe the previous owner disabled all USB ports for security reasons. Or they threw it out because they don’t work.