I have changed the filter but now not working properly
A clogged intake or impeller will still try to suck in water, but will only make noise and actually do nothing, where as a filter with a clogged motor won't turn on at all. The solution to a clogged motor is fairly simple. Just open up the filter, take it apart piece by piece, and unclog it. If you need to, you can use your hands, use lightly compressed air, or if the motor itself is water proof, just blast some water through the motor.
One of the most common problems that people experience with their fish tank filters is that there is a loss of suction, or no suction at all. You see, fish tank filters use something called an impeller that is motor operate. This impeller serves to suck water from your fish tank into the intake tube, through the filter media, and back out the other side in the form of perfectly clean water.
Another pretty serious problem that many people experience with their fish tank filters is that there is an improper flow rate. Now, this is not actually a problem with the filter itself, but it does affect your fish. You see, different fish need different water flow rates, with some liking a heavy flow to swim against and some which can't handle fast flowing water and just get swept around the tank.
Whatever the case may be and whatever the solution to your fish tank filter problem is, you need to take care of it as soon as possible. Without proper filtration your water will suffer from a buildup of waste, chemicals, and toxins, plus it won't be properly oxygenated either, all things which can rather quickly lead to the unfortunate demise of your fish.