Having trouble cocking swarm maxim. - Caliber Gamo USA Hunter Elite .177 Air Rifle with 39x50 IR Scope

Have you allowed water to get into tank?, change fuel and try again.

Its a full version Swarm Assault HD?? Or Just Demo. Because I have full game but Windows 10.. I have Swarm Assault HD Demo but cant find full version.

go into your game video options and set screen display resolution.also make shore your pc can run the game .if no go post back and will look for a better fix .

Each version of Windows has a 'compatibility' mode to accommodate games written for earlier versions. Open your Windows Help menu and just type in 'compatibility' as your search word. 7 has some major changes compared to earlier versions and it may not be possible to 'backdate' for your game but it costs nothing to look.

you have a triger fault its not locking the piston back best and safest bet is a gun smith,, never play with a triger if your not good with guns,

If you are playing in a hi-def mode it is an issue with Capcom because Capcom has a hard time with correcting display in HD.

You should get a good manual. You will need it for specs anyways. It will give you tolerances that you will need to measure to verify if your piston, rings, and cylinder is still usable. I recommend the factory one, but clymer and hayes also make them.

Larvitar can only be found on Route 206. You can only find it if it's in a swarm. Check the in-game TV to check what the day's swarm is.

you have a fuel delivery problem check idle screw adjustment air/fuel screw and idle and transfer ports

The problem is actually the mirror box controlling mechanism and not the shutter it self ,strictly speaking. What is happening is that the locking /unlocking of mirror, when it is cocked, is gummed up by perished rubber bushings and rubber shock dumpers ( life span of 15-20 years max ) .
You need to get to the left hand side of the mirror box ( easy to locate once you take the m. box out ) and clean out with isopropanol ( can use benzine but is unhealthy ). Relatively easy but make a note of where the wiring goes ( shutter and l. meter ). And then also take care with the mirror box -cocking mechanism at the bottom ( draw picture of position before dismantling ).