What to do when VISA credit/debit cards are not recognized by IRCTC site to make reservations. I don't have access to Indian cards.
There is an extensive account of how to buy Indian rail tickets on the website of the man in seat 61.
It is far too long and complex to sumarise here but basically you either use an independent agency which charges a small fee or you register on the official railway site. He also provides a whole list of things which can go wrong with suggested remediation actions.