This same issue happened to me too now.

I can't recall making anything special to cause it. The system has been running since July, and we have used web module, inventory, added products, tested sales quotations etc. We had also built already a website there, all running smoothly. Now I haven't looked for 3 days and during that something has happened, and my web browser is just saying that the "server is not responding". If I try to view via mobile phone browser, it says "Internal Server Error".

In the server logs there is nothing special but it gives quite exactly the same log than here is described as well in this thread. I can't find anything that would be wrong in order to start fixing it. It also has to be something that have gone bad by itself since all the settings have been running few months without problems.

Did you find anything to solve this in your case?

FOUND A SOLUTION TO MY CASE:
Checked once more the config (/etc/odoo-server.conf), and it had a line like this:
db_host = localhost

I changed it to:
db_host = False

After that I restarted the server (sudo /etc/init.d/odoo-server restart). Refreshing the website and it came back after almost a month trying to find a solution! In the end I changed only ONE word in this config. I hope this helps somebody else since it was not easy to find out tips for this issue.

(In my opinion I had done this same config edit earlier though but not sure, at least now this worked!)

It could be a JS conflict. The new module you installed might have some issue in JS. I had faced this issue when I was trying to install an Odoo 8 app into Odoo 9.

To get the exact issue, click the "F12" button in chrome browser when the page starts loading. You will get the issue in console.

Hope this helps!

2016-02-06 12:49:09,582 14946 INFO ? openerp: database: odoo@default:default

It looks to me like the values of default:default after the @ are not correctly replaced.

It should be something like :

database hostname: localhost

database port: 5432

database user: odoo

I'am trying to figure out how to solve this too.