panoram v12 bicycle computer?

The problem may lie in the sensor unit. Open it to see if the battery is connected. Often there will be a small insulator that prevents contact to prevent battery drain. If this is the case, the sensor won't be sending a signal. If the computer is digital wireless, it may need to be set up. There will be a setup mode where the head will search for the signal from the sender. This is how digital wireless computers prevent crosstalk from other senders when you ride with other cyclists. Your computer can only "see" your sender. Read the setup instructions carefully.

Adjust the sensor so that its almost touching the spokes..... It should be about 5-3mm away from spokes.. Also make sure that reflector thing is on a spoke that is on the same side as the sensor

The magnet needs to pass the sensor as close as possible without touching and at the correct spot.