Photoshop CS5 has lost file associations

Question

I recently installed both Photoshop and Dreamweaver CS5, deleting the CS4 versions after installation. I have lost file associations for all Photoshop-related files: eg jpg, tiff, gif and so forth, and the psd extension as vanished altogether. (That means that if you click on a .jpg file, it opens in a free MS utility like Paintshop rather than where you want it to go: in this instance, to Photoshop.)
I have taken the following measures, none of which have worked:
Manually altered the associations in Folder Options. I can browse to photoshop.exe, but nothing happens when I select it.
I have gone into the registry and deleted all associations under the relevant file types, eg .jpg etc. Restarting folder options replaces them exactly as they were, and I still cannot associate anything with Photoshop.
I have run Photoshop from the command prompt with the tag /regserver which ought to re-register it. Nothing happens. (If you want to try this, open the Start > Run box, browse to the .exe file and append (separated by a space) /regserver
I have changed and saved all file associations in the Bridge Options section. They are still there after I restart Bridge, but it has no effect on the overall file associations.
So that leaves me stuck. Both CS5 programs are registered in the program list, and both appear in the Start menu list of programs. Neither appear in the Folder Options list. I am running on XP Pro with today's (16 Sept 2010) MS updates. Can anyone help with this?

Answer 1

Solution
I have found how to fix this, for me at least and on an XP machine. Some users may find the procedure a bit unnerving. You should anyway back up your registry before making these changes.
Start > Run > regedit
Go to:
HKCurrentUser\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts
That will give you a long list of file extensions: ex .jpg, .png
Scroll down to and select the relevant ones, one by one. This is moderately laborious, but what follows is repeated exactly. (I found the .tiff extension was slightly different and left it alone. I never use tiffs so I don't know if it works unchanged.)
When you click on the + box for e.g.  .jpg, two 'folders' open. These are
OpenWithList
This sets the list of potential programs to use for this extension, lettered a,b,c etc.The last entry in the 'folder' is MRUList which sets the priority order for these programs, eg if it has 'bcade' then program 'b' is first, 'c' is second etc. You can edit this order by clicking on it.)
OpenWithProgIds
This stores what kind of image this is. Under .jpg I found that I had 'jpefile' and something like Photoshop.9 (I don't recall exactly.) This refers to a very old  version of Photoshop, certainly not the last one on this machine. All the other relevant image files had much the same terms associated with them. Some had four or five older Photoshop references: you can delete these entirely by right clicking on them. You then right click on the remaining Photoshop reference and alter it to read Photoshop.Image.12 Do not change the identity entry, e.g. the term 'jpefile', as mentioned above.
It is also worth navigating back up to
HKCurrentUser\Software\Adobe\Photoshop
I found that I had reference to five separate versions of Photoshop. You can delete all but (numerically below) the 12.0 folder.
Close regedit and reboot. You will find that Folder associations now recognise Photoshop as a valid program and assign it to the files that you have changed. I have not tried adding to the list in Explorer > Folder associations.
This is pretty shameful, frankly. Adobe's installation program should clean out all preceding registry entries when it de-installs a version. It should most certainly write Photoshop12 refereces when installing. This must be a pretty geenral problem.