I thi9nk your problem is stemming from your previous attempt to install/use OpenSEO.
In reply to:
still got same error:
"can't read /myURL/administrator/components/com_sef/config.sef.php
This is telling me that the Joomla! system is *still* trying to use the OpenSEO component, as that file (even that directory!) is *not* part of the "base" Joomla! install.
In reply to:
I found a freshly downloaded Joomla install package is missing the com_sef folder in both components folders. are they setup on the fly when sef is enabled, perhaps after switching from openSEO to built in sef it got confused, I could delete the com_sef if indeed they are ceated on te fly.
No, I believe they are setup with the *installation* of OpenSEO, and are not needed at all for the "built-in" SEF functionality 
In reply to:
After replacing the missing config.sef.php file from a patch kit (to eliminte ads in some 3rd party seo component.)
I got the new error
Fatal error: Class 'SEFConfig' not found in /myURL/components/com_sef/sef.php on line 1
This is a "step backwards" in troubleshooting, and only complicates the issue(s) you will have to sort out.
My advice to sort this is as follows:
1) Return your Joomla! installation to it's "stock" codebase, *including* the .htaccess file.
2) TO do this you will probably need to *uninstall* any/all OpenSEO realted components/manbots/modules *and* make sure that you have all the original files components of the "core" distribution.
3) Once this is done, and you site is working correctly with *no* "sef stuff", you can test the "built-in" sef urls functionality per instructions in the Joomla! backend (check the option in the global config, and rename the htaccess.txt file to .htaccess).
4) Pay special attention to the .htaccess file at this point, becuase the one you have is very likely "borken." What is placed in theis file (uncommented, or commented out, and entries) is probably screwed up as a result of your different SEO/SEF attempts.
This process should "narrow the possibilities" for problems to occur, and make it *much* easier to sort out problems.
One last "friendly" comment about Joomla! and "search engine friendly/SEO" functionality:
Google, and all other major search engines, do not need any of this stuff to properly index your pages. Actually, the whole "SEF" part of "pretty urls" is of little practical use at present; page titles, content, and links are *far* more important.
That said, you might find that there is little need to install this stuff, and choose to avoid placing the extra load on the server required to rewrite urls.
I don't want to start a SEO debate here (there as many different informed opinions on that as there are ignorant ones!); I'm only sharing my experience with *numerous* Joomla! based sites. I have used the "built-in" SEF urls on occasion, and have yet to see it produce better search rankings than using "stock" Joomla! urls. 
--rlparker