BizTalk host instance unable to start

BizTalk 2013, production server, on windows 2008 R2 64 bit all host instances failed to start,

event log:

Error code 0x80131604, Error description: Exception has been thrown by the target of an invocation.

Googled a bit, there are threads saying it could be BizTalk configuration file issue, I copied one file from a non production server which works but still facing the same issue.

Any idea where to look?

This is - indeed - likely an issue with the configuration file. Most likely, the configuration file does not contain valid XML. Try making a copy of the file and renaming that copy with an .xml extension. Than open it up in a browser or any program that includes an XML parser to see if the XML in the file is valid.

If you are unsure, try putting the XML in your question here (sanitize any senstive data before posting) and we'll take a look.

Any other errors you can see in the event log(s)?