Event Logs in asp.net for portal and server

Question

Hi all...

Once again... In trouble....

Please guide me... How to build event logs in any asp.net c# website ??

Requirement -
1. If a user opens a portal, then the system must capture the page name (index.aspx), the user name, and current time. - Done.

2. If user clicks on any button (say btn_Save, btn_Search), then system much capture the pagename, username, button-id, button-text that was clicked, and time.

In short... How to create such event logs for asp.net website / portals ?

Currently there are 20 web pages in the portal.

Do I need to use System.Diagnostics namespace??
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Other Point -
I have recently faced an incident.
I had uploaded my published files on the iis server.(Remote Desktop Connection)
The system was running smoothly.
But... One other person from other team entered the server and changed the physical path of my portal.
By this, I got many complaints from the users that the site is not working.
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Is there any way in which we can find out who enters the server and make such changes ??
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Is there any way in which we can capture the username/windows name and find the activities done on server ??
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Please guide.

Thank you all in advance...