Component Services (DCOM) window closes by itself

[Demotrion]

Hey guys,
I got this VERY annoying problem:
Lately I downloaded and installed automatic updates for WIN XP sp2.
After rebooting, my AV (Sophos) didn't start, I tried to re-install it, thats is where the real trouble started. "Windows Installer cannot start". I tried every possible solution from Microsoft to tech-support forums. Nothing seems to fix it, and the system shows no signs for a possible reason.
However there's one method I couldn't try: setting DCOM permissions. And guess what, when i open the Component Services and click on the "Computers" folder the whole window suddenly closes by itself.
I'm positive that this is the cause for the initial problem as well, tried 20 different forum threads and they all lead to a dead-end. If the initial problem had a variety of solutions, the last one has none.

So plz, if anyone out there has any ideas Im all open for suggestions.
I'm using WIN XP sp2, Sophos AV, ZoneAlarm Security Suite.
Thanks in advance.