Network connections delayed after system start

After my laptop starts, from boot or restart, hybernation, or sleep, my
wired and wifi network connections are disabled for just over a minute.
After the delay, both devices establish connections automatically and work
as expected.

I've been using Vista on this laptop (dell d620) for about three months, and
this behavior started last week. I can't trace it to any change in
configuration or software or drive changes. When I invoke the Network
Diagnostics tool, it indicates that there is a drive problem. But the driver
works fine (after the minute) and is the one that Vista provided.

Just unplugging and plugging the ethernet cable is handled in a few seconds
(after the minute delay), as is enabling/disabling wifi with the hardware
switch.

I'm a bit stumped for how to diagnose this further. Anyone have any
suggestions? It's also a bit tricky, since I only have about a minute during
which the error condition is present.

Thanks,

--Geoff