my 2000 F250 super duty wont start when you turn the key, it only makes a single "click" sound- all dash/ dummy lights , interior lights come on, have replaced solenoid, starter, battery, alternator

a thin wire goes from the ignition switch to the solenoid , to energize everything, that connection is cut , maybe an old security or rigged shut off switch, can bypass by feeding hot wire to correct thin wire connector on solenoid tail, if doing a touch test with 12 volt wire make sure its in park and hands are clear of fan blades, key off so not to start up till you install a new wire and starter button

unless the engine is seized or froze up

I am having a simeler probably but the alarm system is blinking a code 5 blinks do not know what that mend I have a 2002 Ford f 250 super duty

Also the key fob has stoped working all in one night

Try resetting the computer. disconnect battery and leave headlights on. Wait 15 minutes and reconnect. It should beep at you after a few seconds. My story is with an 06' f250 6.0 diesel.. I shut the truck down at a store. It had ran fine. As I got out the truck honked like I locked the doors, but I hadn't. It wouldn't turn over when I returned 5 minutes later. Also, the fob wouldn't do anything, but the truck seemed like everything else was fine. I disconnected battery 20 minutes, but didn't turn on headlights. That didn't reset. I tried again by leaving it just over an hour. I hooked it up, it beeped at me and started right up. BTW, I saw no obvious codes or error, but I may have just not known how to find them.

I know this answer. You have crossed your wires on the solenoid relay, which will burn up your starter. After it burns up your starter and you go to crank it again all you will get is a single click at the solenoid relay. I know this for a fact