The freezer is working fine, Iv tried rebooting the fridge but it's not cooling at all :( my son had left the fridge open all night....

SOURCE: Freezer left open and now won't work

Try to unplug the unit from the wall and let it sit for a few minutes then plug back in. May reset the door alarm lock out. Also, moisture in the air can be drawn in and freeze up the whole thing. That means turning it off with doors open for about 36 hours... Moisture is a killer in a freezer, freezes and blocks up every air circulation vent, etc.

SOURCE: refrigerator compartment not cooling

If you are sure the fan in the freezer is running and you don't feel any air flow out of the top middle vent inside the fridge section, then the damper motor must be bad. The damper motor is behind that vent cover inside the fridge section.

SOURCE: fridge left open all night and wont cool but the freezer still works.

time for a new fridge

SOURCE: Left door open on freezer last night and now it wont work

turn it off for a day or two let it defrost and then turn it on. it just has frozen up the coil, or the compressor has heated up cause it was working to hard turn it of for a cople of hours to let the compressor cool

SOURCE: Sharp SJ-42-WH self-defrosting fridge. Freezer

I recently had exactly the same problme with this model refrigerator. I found the problem to be the defrost timer. It is located behind the panel on the back of the refrigerator where the mains cord is located, you will need to replace it with the exact same model. I am in Australia and managed to find the exact part on ebay cheaply from a local appliance parts supplier, any appliance parts supplier that deals in Sharp refrigerators should be able to help you.

You will have to defrost the refrigerator overnight again before doing this repair.

Of course there are a couple of other components that could cause this problem, you can acutally check to see if the defrost time is moving by taking note of it's current position and then checking it every thirty minutes or so. If it does not move then it could be faulty, make sure also that power is getting to the timer as well.