Hi everyone, I'm new to this forum and to Arduino. I have started making circuits and they didn't work. But when I moved the whole circuit down a bit more, it worked. I think that the top half of my breadboard is a bit loose and this might be the problem. Where can I purchase a new breadboard and how much is the approximate cost? Thanks!
Welcome to the forum! Glad you got things working. A bad breadboard like that seems a bit unusual, but I guess you never know. Breadboards vary between a few dollars and 8 or 10 dollars, depending on size and where you get them. See this page for a bunch of potential sources: Arduino Playground - HomePage
Some very large breadboards have the + and - lines not connected at the halfway point.
Note the bridge wires at the halfway point. I have a couple of large breadboards like this:
Is it a plain white breadboard with a bus line at the top and bottom?
If so there's the problem, you'd better off with a wooden breadboard a hammer some nails and wire. They're awful and threw out 2 of them, the better quality ones have blue / red stripes for power rails
polymorph:
Some very large breadboards have the + and - lines not connected at the halfway point.Note the bridge wires at the halfway point. I have a couple of large breadboards like this:
Is it surprising that the manufacturer of breadboards with breaks in the rails don't supply some kind of indication to show that it is not continuous? Seems like such a nuisance to me. Why would they want to design it that way?
Foolios:
Is it surprising that the manufacturer of breadboards with breaks in the rails don't supply some kind of indication to show that it is not continuous? Seems like such a nuisance to me. Why would they want to design it that way?
most of large breadboards (all ?) are designed that way . It is useful when your project needs more than one power supply. always easier to add a wire than to cut an inner copper piece 
Is it a plain white breadboard with a bus line at the top and bottom?
If so there's the problem, you'd better off with a wooden breadboard a hammer some nails and wire. They're awful and threw out 2 of them, the better quality ones have blue / red stripes for power rails
You just had bad quality protoboards. I've used protoboards just like that for a very long time, that's what they -all- used to look like.
I will say that I like having both power busses on the top and bottom of the board. But you can find crappy boards like that, too.
Is it surprising that the manufacturer of breadboards with breaks in the rails don't supply some kind of indication to show that it is not continuous? Seems like such a nuisance to me. Why would they want to design it that way?
On my boards, they show it by having the red and blue lines interrupted there, Not very obvious and caused me some consternation until I figured that out.
As for why... Right now I have a 3 stepper motor tester project on a protoboard. The bottom left row of power supply V+ is 12V coming in and has several bypass capacitors, that goes to the Pololu A4988 boards as their VMOT, then into an Arduino Nano's VIN. The Nano's 5V regulator output then goes to the rest of the V+ lines on the protoboard, providing VDD to the A4988s.