Not able to access special characters i.e. @,( etc

I don't know what's wrong with your keyboard, but I will try to show you a way to find out which characters you can enter with it (I'll have to check if this works on newer systems). First, open the System Preferences.

Click the Keyboard icon to get

Make sure that the box to the left of Show Keyboard & Character Viewer in menu bar is checked. If it is, then you should find this symbol in the menu bar. Click on it and choose Show Keyboard Layout in the dopdown menu, which gives you this

and even better, when you press modifier keys, the Keyboard Viewer will show the characters you would get if you pressed a key.