I am having a similar problem.  I had a perfectly good 4.1.2 server running.
I downloaded the 5.0 iso, created the CD, booted the server from
the CD, and chose upgrade.  After about 10 minutes of doing its
thing it said it completed correctly.  I restarted and logged in
as admin.  I tested the Internet connection and all was well. I
then went to one of my Windows boxes and booted it.  I couldn't
get to the Web.  It wasn't even getting an IP from the server.
WINIPCFG showed 169.x.x.x address.  Did a relase all/renew all
and got nothing.  Tried two other of my Windows machines. Same.
Rebooted server. Same.  Intalled the update 1 blade.  Same.
I am writing this from withing the text browser from the admin
console.
Any thoughts?  I checked all the settings and all appears to be
the same as under 4.1.2 but it doesn't work now.