Problem with MS Jet 4.0 Engine (or maybe MDAC 2.81?)

[GM]

Suddenly, I had problems in using MS Access2003 files, in every way:

Access 2003 hang up if i try to open a file.

If i try to open from C# code, i get this error:
"The ordinal 191 could not be located in the dynamic link library
msjet40.dll"

I've already tryed to:

- Using "System Restore":
After system restore, i'm still unable to open mdb files, and even to
reinstal/uninstall Access 2003, so i canceled the restore.

- Reinstall MS Access, or installing MS Office SP2:
In both cases, I get this error during installation:
Error 1904. Setup cannot register
module C:\Program Files\Microsoft Office\OFFICE11\1033\MSRCLR40.DLL. If you
click 'Cancel' or 'Ignore', run Setup again and reinstall or repair your
Access installation. If problem persists, contact Microsoft Product Support
Services (PSS) for assistance. For information about how to contact PSS,
see C:\Program Files\Microsoft Office\OFFICE11\1033\PSS10R.CHM.

- Manually register MSRCLR40.DLL AFTER ignoring the registering problem
during installation of Access 2003:
regsvr32 "c:\Program Files\Microsoft Office\OFFICE11\1033\MSRCLR40.DLL"
results in this error:
LoadLibrary("c:\Program Files\Microsoft Office\OFFICE11\1033\MSRCLR40.DLL")
failed - Invalid access to memory location.

- Reinstall MDAC using MDAC.inf file (as suggested from Microsoft)

- Reinstall JET 4.0 Engine, but how? I have the latest version, and the most
recent version i found on MS site (WindowsXP-KB829558-x86-ENU), cannot be
installed becouse it's the same version. I have to uninstall first.. but
again, how?

Does anybody knows what is this problem related to, exactly?

I've searched on Microsoft Faq, How To and KB, but nothing i've tryed was
succesfull.

Thank to any answer...

 

[GM]

I forget:
I have WinXP SP2 (Not WinXP+SP2. I can't uninstall SP2)