Ubuntu and connections

I'm using a borrowed comp since my Ubuntu box gave up it's ability to connect to net, second time in a year. I'm not sure what's causing that to happen, but the local Ubuntu community is hosting a support day next month. I'll find out then, says me, full of hope. Otherwise, the box is firing just fine, I can do everything but net access. I reckon there's a hidden file that needs editing, or a form field that needs filling in/altering info.

I do know that:

a) The events have occurred twice in the past year.

b) Ubuntu has been the only system present on both occasions.

c) The problem does not happen anytime mid-session. I close down normally the night before, and I'm informed I have no connect at boot-up.

d) All the connections from isp to modem to router to comp have been checked, and are working flawlessly.

In the fullness of time, I will find out, I guess. Meanwhile, staying positive about it!