I can no longer install programs, be they .msi or .exe... I get the same message: "The Windows Installer Service could not be accessed. This can occur if the Windows Installer is not correctly installed. Contact your support personnel for assistance".
Now, I'm aware that there are solutions out there, and I'm fairly sure I've tried them all, although perhaps those solutions could be adapted to Windows 7 Ultimate 64.
I don't have any System Restore points to go back to.
I recently updated to Service Pack 1 (or 2, whichever is the most recent). Could this affect things?
I also seem unable to access the uninstall programs window, and some of my installed programs have started acting up (i.e. not functioning properly or at all).