How many solutions in this code?

I'm having a little memory loss here, and I was hoping I could get some help. Let's say, like the wikileaks document, there was a 256 digit password, and the only possible keys one could use were the letters, numbers, and the space bar. How would one go about finding the number of solutions this password could have. I know that we learned this like 2 years ago in algebra, but I've been thinking for a while and I'm drawing a blank. Hopefully someone can help me out... Also, if you don't feel like doing the math for 256 digits, you could give me a smaller example.