The first thing to check is that there is power reaching the refrigerator. Check to see if any indicator lights or the internal lights are working.
If not there could be a problem with the fuse in the plug or perhaps a circuit breaker or fuse has blown at the fusebox.
If power is reaching the appliance, then try the user instructions or manual. There will often be a toubleshooting section to work through. Should that not provide a solution and if the refrigerator is still under warrantee, then revert back to the manufacturer or place of purchase.
Finally, if that fails, call a qualified/authorised service repair technician to take a look at it.