Why does my 3g dongle say no network??

Since installing some free Avast antivirus last weekend and doing a virus scan, everytime i try to go on the net it says 'no network' if i uninstall 3g and install it again it works for the first time, but once i turn off my computer it goes back to no network! meaning everytime i want to use the net i have to uninstall and install 3g again!!
This is starting to really annoy me so any help would be very greatfull
thanks in advance x

Well it sounds rather as if Avast could be misidentifying some part of the dongle software and removing it. So isn't the solution to uninstall Avast and try one of the other free antivirus alternatives? My personal favourite is Microsoft Security Essentials.

im not very technically minded but i found some adice online before and changed the internet settings on my avast and it seems to be working ok now fingers crossed, thanks for the advice though