Computer Science is a pretty broad topic, as a whole. Are there any areas of specific interest to you? If you're looking to get into programming and haven't tried anything before I'd suggest looking at Python books for beginners that teach with examples. Python is a fantastic language that's great for new programmers, and still used in industry - it's even taking over PHP in a lot of web-development applications.
I'd also suggest something like Essentials of Computer Architecture:
If you're looking at degree-level knowledge and already have a fairly good understanding of hardware, you might be more interested in the above for finding out what your computer is actually doing with the hardware and how operating systems manage everything.