1999 Focus Won't Turnover

Hi,  I have an old 99 Focus 1.8 petrol hatchback. Has worked brilliantly until recently when just refused to turnover so can't start. Key appears to work in ignition barrel, power in battery (lights operate as does radio) but when turn key to position one, light cluster does not operate and nothing happens. If try to turn to position 2, the car alarm system does not deactivate and continues to flash. I have taken the ignition barrel out and it appears to be working correctly. So I am unsure whether it is worth replacing the ignition switch, the transceiver collar that recognises the key or whether it is more likely to be the cluster panel or the computer itself? I have looked at lots of website advice and seems the ignition switch is often an issue - so if this is not working would it cause the key not to turn the cluster panel on? Or alternatively is it more likely the transceiver is not working so that car doesn't recognise the key so will not deactivate alarm and allow cluster panel to come on?  Or am I barking up the wrong tree?  All advice welcome.