I can only suggest you to re-run USB3 step but using an high-quality USB 3.0 pendrive. Sometimes low quality pendrives (such as Sandisk Cruzer USB 2.0) cause upgrade process to hang, while using high-quality pendrives (such as Sandisk Extreme 3.0) makes the upgrade process faster and hassle-free. This comes from my direct experience.
+1
Additional I suggest to use a Windows system to prepare pendrive. Format usb pen to Fat32. Decompress the usb3 folder once more and coppy the decompressed files to the new usb pen. Use windows eject funktion bevor removing the pen.