alarm fault on volvo v70 1998,alarm just not working?

i have a 1998 volvo v70 2.5 t auto,the alarm just doesn't work at all,even the red led on the dash doesn't flash.have checked all the fuses, all are ok.have checked black box above bonnet release,it is still connected.have replaced battery in remote and followed instructions to to reset it to car and still nothing,even the remote central locking wont respond to the remote.but central locking works on key and car starts and runs fine. any ideas would be greatly appreciated.