I have the same issue with Windows Live Mail. Sometimes you click to open and the application seems to hang with nothing really happening.
I have done what most have suggested like reinstalling Essentials and repairing the application. But what appears to be happening is that when it was open on a previous occasion it crashed or never closed right. I end up going into Task Manager and stopping the WLmail.exe proccess. Then it does open. I am guessing it is something to do with this application not closing.
Ever since I got Windows Live, Windows Live Mail has caused nothing but problems in Vista. I use Windows Vista Home Basic on my Dell Inspirion 1525 (2 GHz dual-core processors, 2 gigs RAM). Anyways, onto the issue:
Sometimes (randomly) when I load Windows Live Mail, it won't load at all. Sometimes it'll show the signing in window and then load perfectly fine. However, sometimes it does nothing no matter how many times I open the application. When I go into Task Manager and look at my processes, I have Windows Live Mail processes running for as many times as I opened it. Ending the largest process (the WLM process that is using the most memory) kills them all. From there, WLM starts up fine when I open it again. What could be the problem? It's a minor inconvenience, but it's an inconvenience that shouldn't be there.
For a little extra info, this isn't the only program that's done this. NDSTokyoTrim (a Nintendo DS ROM trimmer) does the same thing. I had to downgrade to the UAC-friendly version to use it at all. However, UAC is disabled in Vista. COM Surrogate is added as an exception in Data Execution Prevention as well as it kept crashing when I open my video folders and the thumbnails are processing. It no longer crashes.
Also, my antivirus (avast! Antivirus Home) is fully updated and I have recently done a virus scan, only to show that I'm completely clean.