I have had issues with LV on the K-1 and it's hard to describe but it appears to be an issue with the mirror, though mine never got as bad as you describe.
When it happens to me I see what looks like a black bracket and I can see through some sections of the bracket to the view through the lens. The first time it occurred to me was in low light so it looked like the screen was on but there was no image.
I could get the camera back to normal by pressing LV again though when I do this there are times where there is an audible difference in the mirror actuation. The issue is most prevalent when I go to use LV whilst in mirror lock up. The odd mirror noise occurs other times when not using LV and mirror lock up so my issue might be completely different.
If you have the camera still turn it on and press LV, if the blacked out LV screen appears take the lens off and see if the mirror is still down. This is what happened in one instance for me (and I need to check this again the next time it happens).
I still need to send my camera back for a check up however as it still works correctly 98% of the time I've put that off for now. When I do I will provide an update on the forum and ask that you do the same if you have any updates.
So far this is the only Pentax DSLR out of four that I've had issues with so whilst this is a pain in the bum I think it's just my turn for the Monday camera.
Tas