Urgent

Hi mate what do you meen you can't get it back on? Have you pushed ure brake pedal while it's off?

Lost the bolts?
 
I'm guessing that you havent pushed the piston back. If you haven't got the tool to do it, use a pair of pliers and push and twist the circular thing behind the brake pad. It's hard to do and hurts your hand but it works.
 
Thanks for the help fellas. All done now, hadnt done the piston. Had no problems with the passenger side one! And didnt touch the piston.