It's hard to say without more about how this happened and what software you are running. For example, many launcher apps let you hide the status bar, so if you are running one of these it might be as simple as checking the launcher's settings. If this is the cause the status bar will be visible when you are running other apps.
Otherwise you could try pulling the battery out for a couple of minutes, or booting into recovery and wiping the cache. To get into recovery, boot while pressing the volume down key, then select recovery from the menu you will see (volume keys to highlight, power to select). When you get a black screen with a red triangle (assuming you are not rooted) use volume up+power to get the recovery menu and wipe cache.
If that doesn't do it, either a factory reset or you could try posting in our main forum where people can discuss it properly and try to work out a solution.
Good luck!