rebuilding the database creates a fresh master, and would not retain the links to teh databases that were there previously.
fortunately for you, the MDF/LDF's will still be in place onthe drives, so you just have to attach them; browse for the mdf files and attatch them one by one.
also, note that all your logins , any linked servers, and any users/roles that used to live in master would be gone and you need to recreate them.
also, changing the collation of the master database does not auto-magically change the collation for databases, or the collation of each varchar/char/nvarchar/nchar/text colaltion in any of those databases;
those have to be fixed individually.
--help us help you! If you post a question, make sure you include a CREATE TABLE... statement and INSERT INTO... statement into that table to give the volunteers here representative data. with your description of the problem, we can provide a tested, verifiable solution to your question! asking the question the right way gets you a tested answer the fastest way possible!