@GDEvans Welcome to Smart Citizen forum; good to see you here !
I agree with @bedinek but have extra to offer with some additional points for checking.
the Urban sensor board plugs into the data board on a connector that has two rows of pins approx 18-20 in total. Please carefully remove the urban board and check that ALL of the pins are straight and aligned in both dimensions perfectly parallel with the others; none bent. Also check the socket on the urban board has no debris or dust in any of the pin holes.
A remedy is to very carefully straighten any bent pins using fine needle nose pliers. Dust or debis can be removed using canned air available from an electronics store.
When inserting the urban board back onto the data board make certain that:
- power (USB, battery) is disconnected first and
- push the two boards together so that there is no air gap between top connector and bottom connector; and the two boards are completely parallel all along; and there are no pins left that are not plugged in.
Only then reconnect the USB.
If, as suggested by @bedinek that oxidation is the issue; then repeated removal and reinsertion of the pins (several times) into the socket can help to remove any such oxidation that might be present.
It’s also possible to examine the pins closely (using magnifying lens; such as your phone camera) look for discolouration that might signal oxidation or a deposit of foreign material. This can be removed using a flat blade ‘jewellers screwdriver’ applied carefully in a scraping action. The pins should be shiny to get good contact.
(yeah I know these things might seem obvious, but even specialists can make mistakes). My experience comes from experience; and I always check my assumptions and the obvious things first.
After that; you can check if the urban board is alive using commands such as ‘sensors’ etc on the interactive user interface via a terminal program on your PC.
NOTE: Please use a PC; not your mobile phone. 
its possible that only some sensors are detected. If some are detected and not others; then that woud indicated one or more chip failures. If ALL are not detected its more likely a broken +Vcc or GND line somewhere.
If there are no sensors at all then I have to say; looks like your board is defective. If you have electronics knowledge and some testing kit such as oscilloscope available then its possible to take it further and diagnose the exact source of the problem.
The first step is to check each one of those pins on the 20 pin connector; see if the voltage expected is present. You can also check the urban board when its plugged in and power is connected; and that +Vcc (+3.3V) is present in all the places it is accessible on the urban board. Unfortunately that is not many due to the design of the board. The Dust sensor connector is about the only place.
But if you have those skills and equipment then perhaps you do not need help with this. I can point out that the circus diagram is provided on the github site that might be a useful resource.
But, at the end of the day; the boards are not economic to repair and individual parts (Data and urban boards) are not sold in shops. Perhaps Fablabs BCN might be able to help you out, but broadly you will need to buy the minimal kit components from the same shop you originally got it from.
