1. The valves may be stuck. Check to make sure that all of the valves are moving freely. If they are stuck, you can try to loosen them by gently tapping them with a mallet or by applying a small amount of oil.
2. The leadpipe may be blocked. Check the leadpipe (the first section of the trumpet that attaches to the mouthpiece) for any obstructions. There may be a dent, a piece of dirt, or a foreign object stuck inside the leadpipe. If you see any obstructions, try to remove them carefully.
3. The mouthpiece may not be properly seated. Make sure that the mouthpiece is properly seated on the leadpipe. If it is not, air will leak out of the sides of the mouthpiece and you will not be able to produce a sound.
4. The trumpet may have a leak. Check the entire trumpet for any leaks. Leaks can occur at any of the joints or seams of the trumpet. If you see any leaks, you can try to seal them with a thin layer of Vaseline or chapstick.
5. Your embouchure may be incorrect. Your embouchure is the way you form your mouth and lips when you play the trumpet. If your embouchure is incorrect, it can prevent air from flowing freely through the trumpet. Try experimenting with different embouchures until you find one that produces a clear and consistent sound.
If you have tried all of these solutions and you are still not able to get air through your trumpet, it is possible that there is a more serious problem with the instrument. In this case, you should take it to a qualified楽器店 or repair technician for further evaluation.