alarm/immobiliser

[Nayls]

Clio 1.2 biarritz (mums)

press the button on the key fob & the doors unlock,soon as you open the door all the light's flash like the alarm is going off but the siren is silent,
tried getting out & starting again but it just keeps doing the same thing!

thought i'd try to start it,it turns over but the immobiliser is still on & it wont activate the fuel pump for it to start.

any ideas what the fault is? could it be the key?

can i override/reset it anyhow?

any help appreciated,

thanks