my norton anti virus download

I just recently reinstalled my NortonAntivirus, but my computer keeps coming up that my Norton is out dated. When I run the check for updates it completes. the download usually completes, but when it comes to the Process part, it comes up failed. I am on dialup for my internet. Is there something I didn't do when downloading my antivirus. I have it on my laptop too and it does the same thing. Sometimes it comes up that I am protected, but within a few minutes it says I am at risk. Please help!!!!! Gloria