hello 
Suppose I have an application in aspnet with sqlserver server in one of 4 gigs of ram and about 2000 users were connected, and the server runs out of resources 
hw would happen: no one will be able to connect to the server or just new users will be able to connect .... 

Something similar happens if no bandwidth required in the server at any given time and all users would connect to the new server or just could not connect?

Hi,

If the server runs out of RAM, it may not be able to function properly and it is hard to say which influence it may cause. If the bandwidth is not enough, it may drop the packets.

Based on my research, when the user connect to the SQL server database, SQL Server Authentication is necessary. I am not sure if the authentication will be failed all or randomly. If the issue is related to SQL, I recommend you to ask in SQL forum below for professional assistance:

http://social.technet.microsoft.com/Forums/sqlserver/en-US/home?category=sqlserver

Best regards,

Susie