It could be one of several reasons:

• Your Vuse GO 5000 may have run out of charge. You may need to recharge the device.
• Your Vuse GO 5000 may have run out of e-liquid. You may responsibly dispose of it.
• The silicone air channel bungs may still be in place; please remove them before use.
• Debris might be blocking the mouthpiece. Clean it with a dry cloth.