I notice that you reside in Turkey, I am not sure if it has been rolled out there yet so you may need to contact your Sony helpdesk for more information on what exact services are available. If they confirm that the PS Store is available, then I would recommend ensuring that you have updated your Tablet to the latest software. Do this via Settings and check for software update.
Once you have done that, visit the Android Market and ensure that you have all apps updated also. If that does not help, switch your Tablet off and try again.
