restict user from entering into page without login

The best way is to implement membership Introduction to Membership[^] which both makes it easy to add login (and related matters) but also handles the redirection for you.

You create a web.config in a folder that forbids access to unauthorized users - it's one line of xml - and it forbids all access to file in that folder or subfolders. Easy!

Look into Form authentication and Authorization. Create a folder and put all resource inside the folder which you want only for logged in users. Protect that folder in Web.Config file:

Look into Form authentication and Authorization. Create a folder and put all resource inside the folder which you want only for logged in users. Protect that folder in Web.Config file:

<location path="[Your folder name]">
	<system.web>
		<authorization>
			<deny users="?" />
		</authorization>
	</system.web>
</location>