How to set date and time on Citreon C5 2005 1.6hdi?

Ive just bought a c5 and just notice there are no manuals for it. The clock and date display are flashing the wrong time and date and no buttons i press work. I also cannot get the radio to work. When i took the car for a test drive they were working perfect but now nothing. Can anyone help with abit of advice of what the best thing to do is?