My guess is that the USB port on the hifi is for a USB memory device. The USB turntable will be designed to provide input to a computer. You could try linking the turntable to a PC/laptop, then connecting the PC/laptop output (headphone socket) to the hi-fi line in and using whatever software came with the turntable to play the records.
Alternatively, get a second-hand hi-fi turntable from one of the auction websites.
