AEA AEA HP Carbine Problem

Hey guys, I have an HP carbine in .25 that has worked well for me but that I hadn’t shot in several months. Well I brought it out recently and meant zero in a red dot I put on it. I forgot my mags so I had to single load it. Shot it 4 times, no problem. Went to fire it again and “click”, nothing happened. Tank still has air (225 bar), so not a valve pin failure (I’ve fixed that problem before). I cock it and the hammer simply isn’t hitting the valve for some reason……..any ideas?