Excellent article: How Windows Installer installs msi
When we launch Windows Installer engine (by running msiexec.exe) we are launching the client process. Client process will launch the Windows service process.
Log investigation is always helpfull. Read about logs here. The article contains link to a document where log file is explained in more details. Here the link for the document ( )
one more article about installation phases
how to read Windows Installer Verbose log article
custom actions article