Whilst attempting to get some software to communicate with MS SQL Server 2012, I decided to try reinstalling SQL.  I removed all the SQL components in add/remove programs and attempted a reinstall.  The installer got part way and then just gave up.

After some Googling, I found that the SQL installer leaves log files in %temp% (SqlSetup.log and SqlSetup_1.log).  SqlSetup_1.log had the following lines:

07/29/2013 12:44:41.033 Error: Failed to launch process
07/29/2013 12:44:41.033 Error: Failed to launch local ScenarioEngine.exe: 0x80070003

Nothing on the net seemed to have a solution (or I need to improve my Google skills).  I found one post about VS2010 problems which seemed vaguely related and decided to remove all the visual studio components to see if that sorted things.  It did.

A dialog from the installer and a more helpful error message would have been nice.