FX Impact MKll wont fire

Out doing some pesting with my impact mk2 today and it stopped firing. Pressure at bottle and reg guages are normal. Hammer cocks and sounds like it drops when trigger is pulled - kind of a click and spring noise. No air us released all mechanical sounds only. Any ideas? I've never had an impact apart, but only because I haven't had to.Thanks.
Sounds like valve broke. If it's broke off,then it will not open to fire when trigger is pulled,even though the hammer is striking it. Only reason why it wouldn't fire if hammer is striking.