I cannot get the computer to register miles when I hook up the system in my garage ...it's a cs100 polar cycle computer. It just stays at zero when I spin the wheel. I took it off my old bike where it worked well and transferred the system to my new bike.

The CS100 is designed to only work off the front wheel. if you are using a trainer where the rear wheel is spinning and the front wheel is stationary you will get no reliable reading. if this was the case on the old bike, you got lucky, the system is not designed to read that way. Too far a distance between sensor and computer.

If you are moving the front wheel, as on rollers, and you are not getting a signal than either the sensor and the magnet are not reading each other (too far away from each other, as an example) or the sensor has a dead battery, or you have the bike sensor turned off in your settings.