Sql-server – How to provide a access to the data base if the user is not having the privilleges

To figure out exactly what is happening, you should check the State that is reported in the message, either in the event log or SQL Server log. For example:

Error: 18456, Severity: 14, State: 8.

The state will usually help narrow down the exact cause. Here is a list of the states and their meanings:

Err  Message
 2   Invalid userid 
 5   Invalid userid
 6   Attempt to use a Windows login name with SQL Authentication
 7   Login disabled or password mismatch
 8   Password mismatch
 9   Invalid password
11   Valid login but server access failure
12   Valid login but server access failure
13   SQL Server service paused
18   Change password required

You've explained that you don't have the SA password and you're not an administrator. In that case, you're going to have to hack your way around it.

See Think Your Windows Administrators Don’t Have Access to SQL Server 2008 by Default? Think Again. by Argenis Fernandez.

That post explains how to impersonate the NT AUTHORITY\SYSTEM login using PsExec (or creating a Windows Scheduled Task running under the SYSTEM account) to create a new login for yourself. Then, you can log in via that new login, and grant your Windows account SA permissions.