> Anyway, on the assumption that something is wrong with the SD card, are
> there are known good SD cards I can buy locally?
>
> The list at http://elinux.org/RPi_SD_cards is not helpful, and seems to be
> full of contradictions.

Make sure your power supply is good.


> I have read stories of people spending lots of money on SD cards and
> finding none of them work, so am a bit nervous about doing this myself.

People buying lots of SD cards and none of them working?  What's the one
common thing amongst all those SD cards?  The power supply.
*** Absolutely correct!

My local Computer tech said to make sure whether the ssd card is 3.3 or 5 volts.
If you plug a 3.3 volt card into a 5 volt power supply it will cook instantly hence people having so many cards instantly die.
If you plug a 5 volt card into a 3.3 volt supply it will be flaky and possibly die over a short time.
The unfortunate thing is, not one of the cards I checked has the voltage marked on it and usually there are no instructions or specifications included.
Check your power supply hard drive connector voltage. Go to manufacturer/supplier web sites and verify the voltage of the card/s you wish to purchase.
Roger