Boot won't lock!

[PsYcHe]

Check that the lock mechanism doesn't have a load of crud embedded in it, give it a good clean with some degreaser, etc. then re-lube and see how that goes. Does the lock work OK if you trigger it manually?

Also check that the striker is adjusted properly, could be that it's shrinking just a fraction in the cold and just stopping short of the contact point it needs.