Charlie from New Jersey writes:
After removing a virus from my computer I’m unable to install anything. A message comes up saying: Windows Installer is missing….I’m using Vista, 32 Home Premium Version. Can you help? Thank you
A damaging virus can leave your computer in shambles. The Windows installer service is a common target of viruses and without it, as you found out, you’re unable to install programs. Luckily, detailed information is available from Microsoft to fix this issue. You can click here  to access the Microsoft support knowledge base article entitled “Error “The Windows Installer Service Could Not Be Accessed” when installing or updating programs on Windows 7 or Windows Vista. “
A word of caution, it is CRITICAL you copy any registry information exactly as it is typed, as a mistype here can prevent the fix from working or worse, cause additional problems. Copying and pasting is a better plan than typing it all out manually. Copy and paste by using the selection tool to choose the text you wish to copy. Then right-click to copy/paste or use the Ctrl + C (copy) or Ctrl + V (paste).