What type of card are you using? Did you format the card prior to using it? Are you shooting RAW or JPEG or RAW + JPEG? What are your exposure settings?
The red light on the back of the camera could mean that it is busy trying to create the image. If it takes a long time, that could indicate the card is not fast enough. Also are you shooting in continuous mode, taking numerous images fast? The buffer could be full, and it's trying to write to the card.
EOS 70D / EOS Rebel t4i / EF-S 18-55mm f3.5-5.6 IS II / EF-S 55-250mm f4-5.6 IS II / Sigma 17-50 f2.8/ Canon EF-S 60mm f2.8 macro/ Canon EF 100mm f2.8 macro/ Tamron 70-300mm / 430EX II Speedlite / Canon FS 300
Canon Pixma MG 3100 / Canon LiDE 2100
Adobe Lightroom 4, Canon DPP, Corel Paintshop Pro X4
