Can not acces joomla backend anymore Err 500

Hi folks,
i just installed a very fresh joo,dle and moodle within my actual joomla. Everything worked fine. but i did unfortunately something in any configuration so i cant acess my backend anymore even the joomla frontend site is still working and my login page for the backend is also showing up correct. but after trying to login i get an error 500.
I use Joomdle in conjunction with a MiJoShop. So last thing i remember was that i thought it might be a good idea to enable the shop as well as a data source in joomla wich did not cause any problem before logging of.
After this configuration i did some course work in moodle to test if a course will will show up in joomla. but unfortunately now i can not acess the backend anymore nore do i have an idea how to start debugging things.
Any help available?
thanks in advance folks and have a sunny day!
carsten

What do you mean with you cannot access?
Do you get any errors, or your password just does not work?

Hi Antonio
thanks for the reply,
my password das work but after providing the credentials i get a server 500 error as described.
nothing else
have a sunny day
carsten

Error 500 is usually a PHP fatal error. You should check you web server logs for some info.

Ok i check the logs but thought that it might not be a problem with php as the frontend and all other sites on my server work well.
i´ll check and be back in aminute
Thanks antonio!

ok there is no error that points to php missconfig in /var/log/apache2/error.log as i can see.
I´m on a plesk so i will see if there are any other logfiles available.

am i right that this error has to show up with a date of execution - so if i try to open the website now the error will show up with a date of now - right ?

This is the only error i can find:

[Thu Jan 14 10:07:49.017607 2016] [ssl:warn] [pid 27620] AH01909: RSA certificate configured for back.iq-guru.com:443 does NOT include an ID which matches the server name

okseems it is a missconfig of the joomdle configuration i did.
i had a backup of my database bevore installing the shop . so i replaced the actual Db with the DB within my backend and now i can acess the backend but all my configurations within the shop have gone.
so i think i will have to go back to the error configured database and look for the settings that cause the problem.
could anybody tell me where joomdle stores the basic settings of its configuration in the databses? perhaps hte missconfig is at the point where i set the mijoshop as datasource for joomdle?
any help appriciated
thanks folks right now!
carsten

Joomdle configuration is saved by Joomla, in extensions table.

As for the error 500: normally, you will see something in Apache error log. If you don't see anything, maybe your server is not configured to properly log errors.

i checked the php.ini and it tells me that it is logging all errors.
is it possible that the error comes from this data source issue as i described ?