Have bought a 8GB SD MC Memory card and can...

If your camera and computer do not support HCSD(High Capacity Secure Digital) they won't. The camera will not recognize it and the computer will generally lock up when you insert the card. I have a 2 year old, a top of the line HP Media Center that doesn't support them. You could try a HCSD USB card reader but the camera still won't read it. Otherwise the card may be bad.