Make sure your Microsoft Account can sync: Settings > email + accounts > hold down on the account name > tap "sync" from the popup menu
If not:
- check that date and time are correct for your location
- remove any restrictions in Data Sense
- Try a Soft Reset (hold Volume Down + Power buttons until the phone reboots - you will not loose data)
- If those fail, go to your Microsoft Account on a PC Browser and change the password, then back n the phone you can put in the new password and that might reset things for you