Checking your camera's manual, it does look like it also has internal memory in it.
You can copy photos from internal memory to a memory card. Look under the Playback section in your manual for how to do that. See page 119 of this manual (the .pdf page is 131):
The way your camera works is it will automatically store photos on a memory card when one is inserted, and use the internal memory if one is not inserted.
If you had a card in it at the time you took those photos, it either wasn't making a good enough connection, was full, or the FAT was corrupted.
I'd make sure to format it using the camera's menu choice for format before using it again. I do that *every* time I reuse a memory card, no exceptions.
See page 172 for how to format both memory cards and internal memory (and I wouldn't format the internal memory before copying the photos in it to a memory card and making sure they're copied to your PC).
Basically, you just press the Menu button, go into Setup, and use the Format choice without a memory card inserted to format the internal memory in the camera, and it will prompt you with a Yes/No choice asking if you want to format the Internal Memory.
To format a memory card, insert the card and when you use the same Format choice from your Setup menu, and it will prompt you for a Yes/No answer to format the card.