does not sound like anything that mistake, but as anyone who receives with the Play Store is important to check:
1) You have a Google account (Gmail =) valid and any problems to login?
2) Can be a single point of failure that is not present after a while?
3) Have you tried from another access to different Internet?
4) If you go to Settings - Applications - All and look for the Google Play Store app, try to delete the data in the same, or even upgrade to the latest version available through an installer in APK format
5) The last option is to reset factory data from Settings - Backup.