Internet connection?

[Thomas Blasejewicz]

Good morning
Running Xubuntu 14.04 (tuxtrans) on a Dell Inspiron 1545.

Now that I have "solved" the update problem, I want to add one or two
things to my fresh installation.
However, I noticed, that the "Software Center" tries to start, but then
simply disappears before anything can happen.
I tried Firefox. Crashes immediately.
(did not try the mailer yet; have not yet set up an account)

But there are no error messages of any sort (except that Firefox asks
me, whether I would like to send a crash report)
I use wired connection. 2-3 other computers going through the same
router have no problems.

As I said above, the "update/upgrade" via a terminal command worked.
So did the "Software update" function.

What am I supposed to look for now?
Thank you.
Thomas