Have the cables moved and are connectors fitted properly?
Are the card and reader contacts clean? Clean the card, put it in and see if it comes out dirty.
How about your power supply? SD card can take several tens of milliamps when starting and then it will just end up in reset loop if the power supply is too weak.
I think 8GB is overkill, but it should work. And the speed of card is irrelevant. It will be accessed in SPI mode. I would use smallest Sandisk or Trancend cards. In my rescue bin I have three no brand and six Kingstons.