I have tried all of the above, no help.

Probably not the best answer out there, but you could upgrade/downgrade your IE browser, reboot, then upgrade/downgrade back. I've seen that fix corruption and bad default settings.

Permissions maybe ?

IE Runs under the context of the current windows user I think, maybe it uses some resource that your account does not have permission to, try adding your account (if you haven't already) to the administrators group on the machine.

If not ...
It sounds like there might be some corruption in the install (the about dialog ... suspicious).

Try downloading the IE setup files for IE7 online and set that up instead or is it vital that you run IE6 on the machine ?

Nevermind...I noticed the Windows 2000 in the question. IE7 doesn't exist for Windows 2000. You could try downgrading the browser to IE 5.5 and then back up to 6.

Indeed, notice the Windows 2000.
And that the PC is being used for years, normal office use, no development, and that this problem now suddenly comes up since a few days, without anything having occurred related to it that I am aware of.
(Permission always has been administrator)

Is the only way to force a re-install of IE6 really to downgrade to 5.5 (horror) ?

Sometimes stuff like this happens with PCs. Improper shutdowns, viruses, failing hardware, system changes, etc. could also be a culprit.

You could try these steps, but I haven't done them myself to confirm: http://www.theeldergeek.com/repair_reinstall_ie_and_oe_6.htm

I'd put this down to an upgrade / patching issue and do a rollback on the server.

Failing that your only option is to try and repair / reinstall using geo's link.

Method 1 of theElderGeek (sfc /scannow), was already implictly run by IEFix.
Anyhow, I did it over : no result.

Before going to his method 2 (enabling reinstalling IE6 by tweeking the register), I looked into SYSTEM32. There, mshtmled.dll was indeed missing.
Now, interestingly I also use the IE editor myself in my own applications, and they indeed do not run anymore on this particular PC.
So I first naively copied mshtmled.dll from the DLLCACHE to SYSTEM32, and registered it successfully : no result to the problem of typing into IE input fields.

Now thinking it over.
(sigh)

Might be worth looking at any other dependencies that IE might be missing or the dependencies of the DLL you just copied.

Sounds like something vitally important is missing somehow ... not a versioning issue is it ?

"not a versioning issue is it ?" : would not know how
did not touch IE for as long as I can remember, windows update is OK, sfc is OK
and, "About Internet Explorer" fails, as mentioned above

How to look for other dependencies ?

yeh thats a hard one ...  hmmmm

Since IE 6 is not installed as part of the OS on win 2k you could completely remove and reinstall it but lets start by seeing if it's repairable.

try this ...

1.  go to add/remove programs
2.  find ie6 and double click.
3.  select repair.
4.  follow the on screen instructions.
5.  reboot the machine

This may require the original windows disc, if it does this likely points at the problem being a vital part of the OS that IE relies on is missing.

The wizard should fix it though.

WOW:
trying to Add/Remove IE6, a MessageBox pops up :
An unexpected error occurred.
Class not registered
res://appwiz.cpl/listbox.htc
Line 225
I click OK, and then the Add/Remove window says
"No programs installed on this computer",
while the listbox shows a list of icons with no labels, as if it wanted to show the installed programs but fails to show their names.

uh oh ...  That don't sound healthy.
Probably about time the server got a rebuild.

Add/Remove progs should never break, I'm inclined to guess virus or similar at this point but it could just be years of degredation.

If I had gotten this far I would likely stick my windows disc in the drive and run an install over the top of the existing install, in theory that should replace any missing files, it's probably a bit extreme at this point though.

Most of our servers are virtualised so in my particular situation it would n't be that hard , I could basically take 2 actions ....

1. rollback the vm to a recent back up that didn't have the issue
2. deploy a new vm from a template and migrate the important stuff over to it.

Not sure what you should do though, I recommend a rebuild though.

OK
trying a fresh install of IE6 first

Wardy_01 :
fresh installed IE6 after tweeking "IsInstalled" -> result : IE6 is healthy again
Thx

Now still Add/Remove program problem left. Looking into it. Google shows I am not the first one with this problem :(

try registering the following dll's

regsvr32 mshtmled.dll
regsvr32 jscript.dll
regsvr32 /i mshtml.dll

I had tried to register these 3 DLL's at the start of this thread, and mshtmled.dll had failed because it was not in system32 anymore for some reason (see above).

After reinstalling IE6 I registered those again -> no result as Add/Remove Programs is concerned, it still fails.

Comparing the registry values with the values they should have according to MS http://support.microsoft.com/?kbid=266668http://support.microsoft.com/?kbid=266668, I notice only 2 differences :

instead of
[HKEY_CLASSES_ROOT\CLSID\{00000535-0000-0010-8000-00AA006D2EA4}\InprocServer32]
 "ThreadingModel"="Apartment"
[HKEY_CLASSES_ROOT\CLSID\{00000535-0000-0010-8000-00AA006D2EA4}\ProgID] "ADODB.Recordset.2.5"

my register has
[HKEY_CLASSES_ROOT\CLSID\{00000535-0000-0010-8000-00AA006D2EA4}\InprocServer32]
 "ThreadingModel"="Both"
[HKEY_CLASSES_ROOT\CLSID\{00000535-0000-0010-8000-00AA006D2EA4}\ProgID] "ADODB.Recordset.2.8"

Could this explain the problem ?