update manager not working

[Thomas]

Good evening
I have kubuntu 14.04, 64-bit version, installed on Dell Inspirion 1545.
This is an "experimental machine", not for production.

I have not used the computer for a few weeks, so I thought, it might be 
time for some "updates".
* The update manager does NOT automatically notifiy me of the presence 
of available updates.
* Started manually (once) it ran for a while and then closed down with 
some error which I could not take notes of quickly enough.
* Restarted update manager -> it "runs" forever without doing anything.
     -> ANY attempts of stopping it, logging out or shutting down using 
keyboard or mouse failed.
     -> the ONLY way out was to cut the power supply.

After a few hours I tried again.
Now it tells me, the last update check is more than a week ago and I 
should click on "Check for updates".
However, there is no such button; at least I cannot find it anywhere.

Is there any chance of making kubuntu do what it is supposed to do?
I mean WITHOUT all the extremely high-level computer skills that are 
usually suggested and way beyong my capabilities ...

Thank you.
Thomas