Not sure exactly where you're stuck. but here goes:
To get tenshi, you have to have every switch turned off, then you use the 12F relay point, and backtrack down the stairs you took to get to the relay point for the first time.
To complete the 3 floors as a whole. You use the relay point, have all switches turned on (the all on switch is right there anyway), pass the triple lock orb thingie, and turn all the switches off (via new switches that you can only access after the relay point), and I think you have to turn them on again. It's really hard to explain.
The key is to treat everything before the relay point completely seperate from everything after, it'll save you a huge headache if you avoid treating it all as one big area.
So get all the corners and secrets before the relay point, ignore the all on switch btw, and then pretend everything up to that point never existed when you're ready to finish the floor (the stuff after). I seem to recall you had to turn the first switch off, then on again, before you could turn the 3rd switch off for the first time.