Go to your local user folder and then to the appdata - local folder.
Should be a file in there called desktop.ini
Contents should be ...
[.ShellClassInfo]
IconResource=C:\Windows\system32\SHELL32.dll,31
[ViewState]
Mode=
Vid=
FolderType=Generic
Mine had lost the 1 making it just 3.
When i'd changed this and rebooted, I was able to set all of my missing icons again, all of the windows explorer 'default folder view icons' returned and all of my corrupted system icons in control panel and administrative tools / computer management returned. Interestingly enough, my documents and settings folder as well as one or two other folders had the recycle bin icon but I was then able to reset them back to default.
I still don't have a visible iconcache.db file and yes, i've looked in all the hidden and system places.
How did i work the above out?
Created a new user and checked with new files appeared in the new user account that for whatever reason didn't exist in mine.
Hopefully that helps a few of you out, it's been bugging me for months!
Cheers,
Patrick