I want to install kickout flashing to an existing house where the gutter for a first story roof buts into the siding of the wall for a second story. I want to deflect the first story roof water into the gutter instead of flowing down the hardboard horizontal lap siding. Do I have to remove the siding and shingles to install the kickout flashing, or is there a trick to doing this.

I was sitting in my family room, which is in the basement and noticed a lot of water running down my walls and collecting on my floor. The trickles of water spread about 5 feet. When I reached up and touched the ceiling where it was wet, the water overflowed and spilled out even more. I went to the bedroom directly above the family room and discovered that there was water running down the doorway of the closet. Not near as much as downstairs and hardly anything pooled on the floor. There are hardwood floors in that room. The ceiling in the closet looks like it's water damaged so I know the leak is there, but there is no plumbing near this room. We had a very heavy snowfall of 75 centimetres shortly before this which was followed but a couple of beautiful days which caused the snow to melt. I have a sick gut feeling that my roof is leaking. This house is 26 years old and the roof has never been redone. How likely is it that the whole roof needs to be replaced? Is there a ball park figure that I should expect to pay? How much damage can be done to the rest of the home because of this? I don't think this is the first time this has happens in this home because I can see water damage on the ceiling in the bedroom and family room, in the same places I saw the water too. I'm freaking out!