The 3 amp fuse on the circuit board keeps blowing. Someone please help me.

Check, and replace contactor in outdoor if it is blowing on ac, or check to see the wire was not hit with the weed eater.

I am not getting any power to the unit. When I change the fuse it automatically blows. I did check to see if hit by the weed eater and that a negative.

Does the fuse blow with the t-stat off?

Yes

Next thing to do would be to disconnect the t-stat wires from the control board. Then try the fuse and see if it blows

See the air conditioner worked a couple of weeks ago but it got cool and I turned it off and now its doing this

And yes it still blows

If the fuse is blowing with the t-stat wires removed from the control board then the board must be touching the metal, or the bad is bad and shorted out.