Restore Database wizard won't open in SSMS 2014
I have seen that behavior myself in both SSMS 2012 and SSMS 2014. What it typically means is that the backup / restore history for the database is very long and it is taking a long time for the wizard to come up, because it needs to read the entire history.

Make sure you have a maintenance plan that truncates the history. To find out, run this query:

SELECT TOP 1 backup_start_date
FROM msdb.dbo.backupset WITH (NOLOCK)
ORDER BY backup_set_id ASC


That query will be quick, since it's sorted by the primary clustered key of the table. If you've got more than a month or two of history in there, it's probably time to clear it out. (Keep in mind that clearing the history will involve locks, so it can be a slow process if you're doing backups at the same time, or if your MSDB is on slow storage.)