[tsac]

If your saying theme setting then I would suggest first powering down the phone by pulling the battery, wait for a couple of minutes and replace. If that does not work then entering the phone password wrong multiple times will cause a reset to factory.
You can use the Blackberry program "desktop manager" to do a backup for your contacts is needed.
You can also try looking for the settings again and do a theme switch. The settings may be there but under another option or view.
Using DM will also allow you to reload the OS back to basic.
DO NOT RELOAD APPS YOU HAVE ADDED because one may be causing this issue.

Reset methods

First method:
1.Power on the cell phone after battery pull
Hard Reset BLACKBERRY 7100t
2.Now go to Options -> Security -> Wipe handheld.
3.Then type the word BlackBerry.
4.Next your phone will reboots and resets.

Second method:
1.Check your phone if is it on.
2.Then go to Options -> Security -> Set a password.
3.Now enter this incorrectly 10 times. and follow the prompts.
4.After the 10th time, it will reset the BB, wiping out all customer data.