Can't install any programs

Hi!

I just installed VISTA Ultimate 64-bit on a Quad Core 6600, eVGA 8800 GT, 2 GB RAM, 1 TB (Raid 0+1), ASUS P5N-T Deluxe computer.

I am having two issues:

1. When I go to run Windows updates, several updates will fail. Along with others, these are the "Definition Update for Windows Defender" and "Windows Malicious Software Removal Tool x64). The error code is 80200053.

2. When I try to install any non-Microsoft application such as FireFox, WinZIP, Adobe Reader, I get an APPCRASH. VISTA tells me that the application has stopped working, and it stops the application.

Can someone PLEASE help? I'm going crazy trying to get my system to work, and I can't seem to install any applications.

Thanks in advance!

Have you checked for any viruses? It sounds to me like perhaps ther is something on the system that is preventing the updates to Defender, and the Malicious Software Removal Tool.

But seeing as installs are also failing, it's possible that the Windows Installer Service is corrupt. Try manually downloading an update for this to try an fix it.

I will try and check for viruses. However, last night, I did a clean install, and I'm still seeing the same issues.

How do I manually install the Windows Installer service?