OK, lets first check to see how the Time Capsule is set up.
Open AirPort Utility (Finder > Applications > Utilities > AirPort Utility)
Click on the picture of the Time Capsule
Click Edit in the smaller window that appears
Click the Wireless tab at the top of the next window
Check the setting for Network Mode
What is the setting that you see there?
Two possible correct settings would be.......
1) Create a wireless network.......meaning that the Time Capsule is broadcasting a wireless signal that could be used by other wireless devices to connect
2) Off......meaning that the wireless function of the Time Capsule is turned "off", so the Time Capsule is acting as a wired device only
IF......the Time Capsule really were connected via your wireless network.......then you would see a setting of "Join a wireless network".
Please report on your results.