The only way you can find whether your 128GB flash drive is a fake or not is the price you paid for it and the place where you bought it.
If you have paid more than $100 as per Jumanji's link (PNY) and bought it at a respectable store, then it could be a genuine one. Sometimes even the genuine ones fail. But they carry a warranty and all you have to do is return the flash drive to the original seller and you will get a replacemant. Once I returned a non working Transcend flash drive after six months and got a replacement without any squabble. The only requirement is that the serial no. on the device should be intact.
If you have paid an unbelievably low price for this flash drive, then 99% it is a fake. Definitely it does not carry any warannty. Don't bother to repair it and chuck it out in the trashcan.