Rory
What I know about the Siemens 505 range you could write on the back of a postage stamp in block capitals, but I will try to help you out here.
Are the I/O's in question local or remote? If they are local, are there dip switchs that have to be set? if so are they correct?
Are your 'input changes' showing up on the input card, in other words is the card wired correctly?
If you can answer these questions, then post the answers back here and I will have another try, or hopefully maybe one of the other regulars will chip in with some advice.
I think that you need to check that you have addressed the inputs correctly.
Hope this in some way goes to help you
Paul