installer does not find a network - but a live system does ... wtf?

[Andi Meier]

*bump*

in short terms: Ubuntu cannot find any working network although it is there. Here come the symptoms:

(everything on the same PC:)

  (case a) boot Ubuntu Live 10.04 from USB flash drive => Ubuntu is able to retrieve IP address via DHCP => OK

  (case b) boot Ubuntu 10.04 from harddrive (installed system) => Ubuntu is not able to find ANY DHCP server, is
      not even able to detect any network, also with static IP it is not able to find any network

  (case c) launch Ubuntu 10.04 installer from USB flash drive => same as (case b): unable to find any network or any DHCP server

How is this possible? I don't have a clue.

Cheers,
Andi