Hello Anju
When you just log in, you get in to a page called Manage Account Settings in that page a list starting with View Profile, on that list the 9 the one will be My Messages Just click on that, yo enter in to your message inbox
In any other time while surfing SPK,if you wish to see the message inbox, click on Your User name that is shown under Online members in the left of your screen
Or else you want to get in to the Manage Account Settings page click on Your use name written under my profile below online members
Hope you got it