WLM not starting msmail.dll not initialised

Hi there, I'm having a problem with Windows Live Mail not starting. I get an error message telling me it may not be installed correctly (error: 0x80041161) and msmail.dll may not be installed correctly.
<ignore>It has been working fine up till now. It does open when I browse to the program folder (rather than using start menu or desktop shortcuts), but it doesn't load any of my account settings, contacts or messages.</ignore> -Edit: I've just realised I'd opened WinMail not WLM.

If it's relevant I've had problems with other programs (mostly Microsoft) starting up. So far today I've had problems with:
Excel 2003
Word 2003
Internet Explorer 7
Windows Contacts
Windows Live Photo Gallery
Blocklist Manager

I'm also having problems installing the latest Windows update (KB942615- Cumulative update for IE7), getting the error number 80073712.

Since I'm having so many problems at the same time I don't know where to start! Thanks for your time.

Nevermind, formatted hard drive and reinstalled Vista.

Sorry to bump this but this problem has resurfaced so ignore my last post. It's the same programs. It makes no difference whether I start them from their folders or shortcuts.

I tried repairing Windows Live Mail, Photo Gallery and Writer but got an error message telling me they weren't installed properly. Same when I tried to uninstall. They were working fine!

What could be causing this? What should I do? I've only just started to get my programs and files set up again after my last format so don't want to have to do it again.

Edit: I forgot to mention when I try to reinstall Windows Live Suite I get the error message:
"Code: 0x80070641
Description: This installer service could not be accessed. This can occur if the Windows Installer is not correctly installed. Contact your support personnel for assistance"