Hello,
not sure if you are still having this problem, but if you are, heres something I posted in another tread with the same issue.
Hello, I am the owner of the previuos post about the G17. While fixing it, I, of course, took it apart many times. Once, when I did, I left the recoil spring out, causing the same problem as you have. Have you disassembled it at all?
If that spring is left out, the hammer that releases gas wont come back, and all the gas vents out. Could this be your problem?