Open AirPort Utility, click on the Time Capsule icon, then click Edit in the smaller window that appears
Click the Network tab at the top of the next window
Make sure that the setting for Router Mode is set to "Off (Bridge Mode)'
If you want to turn off the wireless function on the Time Capsule, click the Wireless tab at the top of the window
Change the setting for Network Mode to Off
Click Update at the lower right of the window and allow a full minute for the Time Capsule to restart
You should be all set
If you are using Time Machine to back up to the Time Capsule, you may need to reset things again in Time Machine Preferences to get backups going again. Post back if you are having difficulty getting backups started back up again.