Do you have any other USB devices that you can test via the problem USB ports?
Is the following link the Quick Start Guide applicable to your microphone?
https://s3.amazonaws.com/cd.bluemic.com/pdf/yeti-nano/Yeti_Nano_QuickStart_REV_C_EN.pdf
If I follow correctly, your earbuds work when plugged into the microphone's headphone output ( audio 3.5mm jack) - correct? And the microphone is plugged into the computer via a USB port - correct?
Try mapping out the problem, for example:
Earbuds to microphone audio 3.5 mm jack = no hiss.
Earbuds to computer USB jack = hiss.
Headphones to microphone 3.5 mm jack = hiss
Headphones to computer USB jack = hiss.
Do other USB peripherals work in the tested USB ports? Likewise map out what works and does not work.
Not sure what may have been damaged and what may be the extent of the damage.