Sometimes the news server's article database needs to be reset (after an update or a system crash). At that point all the message numbers get reset.
Each message that comes in gets numbered by our news server. This is what allows you to only get new articles in your news reader; your news program stores the numbers of the articles you read. To save space, it consolidates numbers.
For example, say you just subscribed to a new group and read all the articles up to 204 as well as 256, 264, and 301. Instead of storing over 200 numbers in a file, it abreviates like the following:
1-204, 256,264,301Thus your news reader looks at the file and sees you've read all the messages from 1 to 204 as well as the additional three messages. So the news reader knows not to get those messages.
Now, when the article database on the news server is reset, all the incoming articles get new numbers--typically lower than what they where before.
When your news reader goes to get new articles, it sees that you've read up a certain number (say 1045). However, that was in the old database on the news server. The new one might have started numbering articles all the way back to #1. Thus new articles are coming in, but you don't see them because your news reader thinks you've already read them.
The solution is simple, if ineligant. It's to make your news reader forget all the numbers it's stored and start again. Doing this varies from program to program. Below are instructions for various supported newsreaders. For anything not covered, unsubscribing from the group and resubscribing typically solves the problem.
Note: You will probably see old articles you've already read in the list once you've reset the newsgroup.