We had the same problem wit our exactly 2 year old S5, our retailer sent us a link to ultimaker-repair instructions, which are aimed at "professionals", because of some potentially deadly high voltage under the cover.
So we followed the instructions, but unfortunately the provided "restore"-Image wasn't recognized by the printer/controller board (tried multiple sd-cards and different variants to flash the image).
Did some google-research, and somewhere in the forums a link to an older recovery-firmware was found. Copied the image to an sd-card and the bootloader instantly recognized the card and did a complete recovery from the card. After that it was easy to upgrade to the actual 6.1 firmware per USB-stick.
So basically you should contact your retailer, get some repair instructions after admitting you know what to do, and if this doesn't work, send the printer back or come back here.