please help my digi card wont work any ideas. put it in and nothing. 
Try pressing the OK button several times. If that doesn’t work it is likely it is faulty. You need to call 0300 790 6109 and report the problem and apply for a replacement within 7 days. You can continue to drive for 15 days by taking a printout at the beginning and end of each shift and entering your name and driver licence number on each.
HERE is a pdf of the form you need so you can print it off.
thanx 
Try the card in a different vehicle to determine whether ther card is at fault, or the machine itself , before you do anything else.