Ugraded to 12.04 now my internet is inconsistant

Back in 2008 I installed Kubuntu on my main computer with the latest and greatest version and untill last week was forbidden by my wife from messing with what she thought was the perfect desktop. Last week when hulu stoped supporting firefox 3 she gave me the greenlight to upgrade.

Installed Kubuntu 12.04 yesterday with no problems except my internet has gone wonky. It'll work for 20-30 minutes nice and fast (faster then it was before the upgrade) then it just stops working and every website I point it at pulls up the error message "server can't be found' the network shows as being conected the modem says its connected and the system monitor says I've got plenty of ram and CPU capacity.the problem is consistant with firefox and rekonq and isn't fixed by just closing and restarting the program.

I'm hoping its something simple since I haven't had to really get into the guts of my machine for awhile and my comand line skills have gotten pretty rusty.

Note: I'm using a wired conection Not wifi

From the lack of response I guess I'm the only one having this problem. As an update I have managed to download a few ISO's of different distros and have been trying them out to see if its just a 12.04 issue.

There have been quite a few postings about problems with 12.04 and networking - probably why no-one is replying, since you include no hardware or driver details. If you bother to look, you'll find a number of postings with hardware and driver posted (look for lspci listings, and use sudo to run, as otherwise some detail will not get supplied.

I really don't see why you didn't just get a more recent FireFox, and not get involved with full upgrades (which are not unknown for giving problems)