So this is the trouble i have had with my windows 7 Build 7600. Whenever my clock ticks 12 am and the computer is still on, somehow the time and date disappear and this is how my clock looks for the remaining 24 hours and then after 24 hours its back to normal i.e. with the date. Hope This picture Gives you some idea [URL=http://img32.imageshack.us/i/clockj.jpg/]
I'm guessing that this has to do with regional settings, since I notice the EN there. Here are my regional settings that do not exhibit the same problem you're having. Try to copy them and apply, reboot. There's also quite a few settings to look at when you hit the additional settings button, including reset buttons.
Here is related info. It doesn't describe why this is happening automatically when you don't want it to, but may help you figure things out. Check the short date in date tab.