catblaster: It sounds like that sear spring may be caught up somewhere. Remove the slide. Remove the mainspring housing, then cock the hammer back, remove the slide safety (you may have to wiggle that a bit) then remove the grip safety, then the hammer. Your mainspring should just about fall out if it hasn't already. Now, remove the sear, sear spring and plunger.
Set the sear spring aside. Reassmeble the sear and plunger without the spring. Reinstall the hammer, then the grip safety, then the slide safety. Make certain the hammer is down on the firing pin and reinstall the mainspring housing (use a punch or nail to hold the housing in place until you see that the hammer and sear mechanism are working properly). That should complete your necessary frame reassmebly. Note that you have left the sear spring out. I removed the one from my Colt Gold Cup and she shot better than ever. Hope this works for you. Mikey.