.net application hangs in iis7.0 at peak time randomly

we have our own webserver in that internal applications are hosted in that one of the application will be used at peak time by around 300 employees

this application get hangs some times in peak time

server details as follows: windows server 2008 standard IIS 7.0 .net framework 4.0 sql server 2005

I have created one application pool for 2 .net internal applications in same configuration as specified above. the other application will not get hangs in peak time and running smooth with similar number of users.

I have one doubt is some one forcefully stopping the application to run slow and get hangs .

Please let us know what will be the exact solution as i am getting this issue since 2 years and i googled and done changes in queries, IIS settings and code standards. but still the same problem persists making my life disaster.

some times i get errors as 1. network tcp_errors server may busy or server is down 2. in event logs login failure for sa 3. some times CPU usage will be 100% at peak time