This is a Ground Fault Circuit Interrupter, GFCI. You will have two or three wires feeding this receptacle, black which is sending the electricity. White which is returning the electricity to the main circuit panel and probably a ground wire which is only for problems.

The black and white have to balance or the GFCI will trip and cut the electricity before someone gets hurt.

Now, unplug everything on this receptacle and any other receptacles that this one may feed, then hit reset. If it will reset plug everything back in one at a time and run each device as you plug it in. If it trips on any device then that device should be replaced.

If it will not reset at all turn off the breaker and remove the GFCI from the box and see if any of the wires could be touching someplace where they should not.

If nothing looks wrong then a new GFCI could be in order.

This is a Ground Fault Circuit Interrupter (GFCI) receptacle. Its internal circuitry compares the current (amperage) in the 'hot' wire to the current in the 'neutral' wire. A miniscule difference will cause the GFCI to 'trip' because that means the current has taken a wrong path, or else the GFCI receptacle itself is faulty and needs to be replaced.
I'd first take off the coverplate and ensure the receptacle box has no moisture or foreign material in it, especially anything in contact with the receptacle itself.

Thanks. Will try it

Prepare to replace the whole GFCI. Considering your symptoms, I cannot think of anything other than an internal problem that would cause the GFCI to trip.

I'm with Tim, the GFI is simply bad.