Couldn't upgrade from 10.6.8 to new version

Dear Madam/Sir,

I have problem in upgrading my Macbook Pro. It is OS 10.6.8 and I couldn't update it to any other new versin. Today I tried to upgrade to Mavericks but the same problem occured. It's like a closed ring which I couldn't get out of it. The icon for the new OS X appeared with (open in Macbook store) and when I click over it, I go again to the store.!!!

The apple store icon in the dock couldn't be open and this notice appeared without any progress:

One Moment Please.

Connecting to the iTunes Store.

Loading

If iTunes doesn't open, click the iTunes application icon in your Dock or Windows Task Bar. To download iTunes, please click here.

I hope that you could advise me to the correct way to solve this problem.

Accept my best regards.

Yours

Ali