c&k 700L?

I have a C&K 700L which apears to be ok, however when i set the alarm, it doesnt set. it doesnt reset or part set, nothing at all. I type in my alarm code which makes a noise as i press the buttons. But it doesnt then set with the long chyme. I dont recall having a power cut and there are no flashing lights. the fuse isnt burnt out and everything looks ok in the box. Please help