I had not fired my Sigma 9mm in so long that I forgot that I had to pull the trigger before trying to remove the slide. Now the trigger WON'T pull (and the slide won't release). Is there something I can do to fix that problem or do I need to take it to a gunsmith?

The slide won't release? Is it in the back position?

I think I know what uv done. Pull down on the take down levers and see if the slide will go rearward...is that the problem?

pull the slide back remove the end plate and the striker see if it will then move forward for take down while pull the takedown tab