Thank you for coming back and confirming the cause of the problem, although the credit should really go to @van_der_decken as he pointed out this possibility first in post #13.
Since the IC that was initially used appears to have drawn sufficient current to deprive the UNO of power and prevent it from working properly, it effectively caused a short across the USB power rails. USB does have a protection mechanism and can shut down in such an event, but it is also possible that this IC has now been damaged and may not work as expected in a future project and may therefore need to be replaced.