If nothing at all happens?
Well, obviously the tank could be empty. I've made that mistake a few times. ie taken the gun apart, check everything... a few times before I realized I had an empty tank.
But other things can cause that. An obstruction on the bolt, like a broken shell, or broken fingers can cause that. Or if you have a port-screw that is too long, hitting the bolt.
For the hammer, a common mistake is to replace the 10/32 valve screws with the longer ones used for the panels. They push against the cupseal and keep it from moving. Likewise, some aftermarket cupseals were 2-piece. They could become seperated, and lodge itself in front of the hammer.
And might be the ASA. Some VM asas had a small depressor. If the HPA tank also had a small pin-valve, its possible that they just don't make enough contact to open the valve? Like said above, you can tell that by gasing up with the valve removed to see if it at least gets pressurized.
BUT, if it does at least "pop" when you pull the trigger? But not enough to recock? Similar issues as above. Likely there is an obstruction. Sometimes you can isolate by first removing the bolt, and see if the problem goes away. Does it still have the spring guide? what parts are still original?
__________________ www.montneel.com "the evidence strongly suggests that neither Billy nor Adam (Smart Parts) could have invented the electronic paintgun" -Garr M. King, U.S. Judge