Is it hard to go to a top college in computer science like berkeley and have no knowledge whatsoever, and still be able to perform well.
Berkeley specifically has an introductory course, CS 10, that students can take before starting in the CS major sequence with CS 61A, if they do not feel that they can handle CS 61A from the start.
CS 10: http://cs10.org/sp15/
CS 61A: http://www-inst.eecs.berkeley.edu/~cs61a/fa14/about.html
Other schools may also have different introductory sequences or points in the introductory sequence that students can choose.
At the very elite CS schools, there are definitely students who start the major with virtually zero experience in computer science. It’s very possible, and the programs are designed to help you start from scratch.
That said, you should probably learn some on your own first. At the very least, it would help you decide if you really want to go into computer science.