Help - Leaf buds dying
 

I was given a Japanese Maple tree as a gift in the Autumn. It had leaves when it came, and was kept inside over Winter (in an unheated part of the house). As Spring arrived, I put it outside.

Since then it has produced leaf buds several times (bright red tips to the branches). However these don't seem to open, but look as if they are drying out and dying. I have been watering the tree when it seems to need it - trying not to let the soil dry out, but also not watering it when it is already quite wet. I haven't added any fertiliser as I read that you should only fertilise a healthy tree with leaves.

On a possibly unrelated note, the tree has a ring about a cm wide around part of the trunk where it looks like the bark has split all the way around. I think it was like this when I was given it. Since the spring, part of this looks like it has started healing over. Any ideas what it is?

Any advice for keeping my tree alive and producing leaves would be much appreciated.