First, make sure that you didn't accidentally change your phone's configuration. Tap the Contacts app, go to the Settings menu and make sure that All Contacts are being displayed.
Also, in case you have a Google account, there's a very good chance that your contacts have been backed up via Gmail. Just log into your Gmail account from your PC, click on the big Gmail button on the upper-left side and go to Contacts. In the new tab that opens up, look at the left-side pane for a button that says More. Press it, then click on Undo changes and see if you can get back your contacts that way.
Lastly, there's an application called MobiKin Doctor for Android that works with phones that aren't rooted. All you have to do is to install the tool, connect your phone to your computer, then launch MobiKin Doctor for Android and follow the steps form its wizard-like interface.