Seriously, mine did that, but it popped up a few seconds later. There's no need for background tasks to be on because that's only related to weather, stocks, and news. The clock is independent of that.
Before you hard reset your phone you can save most of your stuff by backing it up in the skydrive... Make one if you haven't, free 7 gb
Its under Settings < backup. There are multiple things you could back up but I highly recommend the one for the apps, cause its pain it the A** to re-download everything