I have a weird example. My SD card was working perfectly fine until i wanted to change disty on it. It says image is loaded successfully, but not booting at all. I tried a 1GB SD card to test and that card is booting fine. Is there any chance to fix other card, it's an 8GB SanDisk SD card?
Try with multiple SD cards with multiple distros. If another SD card does not work, your RPi may be damaged. If another card works, well your SD card is working. I highly doubt your RPi is the problem, since there was a problem with one SD card not another.