The cute litte Windows Explorer Shell Overlay Icons of TortoiseSVN (you know those red, green, blue, etc. icons) that indicate the SVN state of your files or folders are missing.
Your are using a 64-bit version of Microsoft Windows 7.
The 64-bit versions of Windows 7 can only handle a total of 15 overlay icon handler.
The resolution to edit the registry, as described in this article on Stack Overflow did not work on my machine.
What actually helped was that I updated to the latest version of TortoiseSVN and then used Autoruns from Sysinternals to remove all the Shell overlay icon identifiers except those of TortoiseSVN:
In my case there were lots of those ugly Groove entries (installed by Microsoft Office 2010) and some Dropbox entries.
After unchecking and rebooting my machine, the TortoiseSVN icons appeared again.
You can get Autoruns directly from the URL http://live.sysinternals.com/autoruns.exe without the need to install anything.