This has been the one ongoing problem with my '04 Limited XF. Will start every day for weeks and then the one day I really want to take it out for a drive and it won't start. Sometimes I can wait 20 minutes and it will start; sometimes a couple of hours; sometimes the next day. Have taken it in twice to 2 different dealers (both very good BTW). They have tested everything and can't find anything wrong. The dealer last week told me the next time it happens to have it towed in immediately so they can check it out. I really worry about loading my XF on a flatbed and taking it out there. With my luck it will be towed/carried to the dealer and it will start right up. Sounds just like your problem - all lights on the dash come on, can even hear the engine fan starting up but not a sound from the starter, no clicking, nothing. Again, wait a while and it starts right up. Very annoying and each time it happens I start looking on the web for a new car. Then, once it starts up again, I can't believe I even thought about getting something else.