My refrigerator is on but its not cold how can i fix it????

A refrigerator not cooling properly could have a number of causes. The fact that it is still on (the compressor is still humming) helps to narrow those causes down quite a bit.

The problem is most likely due to ice or dust or possibly both.

If there is an excess buildup of ice in the freezer, you may have found the problem. Ice can block the fan and coils from doing their job. Get rid of the ice with either a carefully utilized hair dryer or by turning the thermostat off and leaving the freezer door open until all the ice has melted away. This will take a number of hours and may require towels to handle the resulting melted ice.

With the ice melted, return the thermostat to its normal setting and close the freezer. If ice buildup was the problem, the refrigerator should be cooling properly. If the refrigerator is still not cooling, there is likely a problem with the defrost system other than ice. This will require a trained professional to evaluate and repair.

There is a set of coils, usually on the underneath of the appliance that needs routine cleaning to prevent a buildup of lint, dust, etc. A brush and vacuum do the job nicely. Be careful of sharp edges, especially if the removal of a kick plate is necessary.