This is a very important piece of information that could have helped you avoid a lot of grief and various posts. This is the original boot loader (used on all Nano’s sold by Seeed as far as I know). It means you can forget about the HEX files and USB drive for firmware upgrade which some competitors’ products started using recently. You should use either ST Dfuse Demo or dfu-util, as described in the wiki.
When you plug it into your computer, a USB device of vendor ID = 0x0483 and product ID = 0xdf11 should appear (you can see it with lsusb on Linux or Mac, with some utility like usbview on Windows (or dig through the Device Manager). If not, the upgrading tools won’t see it, and you most likely have a hardware problem.