Several things could be the problem. Scanner programming, the power wire to the scanner and so on.
Like mentioned above, you need to confirm that the scanner is working properly to determine whether it's a scanner issue, or an issue with the vehicle.
If the scanner works okay in the desk top mode (AC power cord, regular antenna), then you know the scanner isn't the issue.
Once you confirm the scanner is working then bring it to the vehicle. Use an extension cord for power to the AC adapter and connect the scanner to the vehicle's scanner antenna. If that works, then try the actual 12 volt power supply.