Is the battery good? Is it charged? Are the connections all tight?
Did you try jumping the starter relay/solenoid? Just because it's clicking doesn't mean it's actually making the connection inside. Jump it with a heavy gauge wire or a screwdriver, a small wire will get really hot on your fingers if you hold it there too long. If you don't have a heavy gauge wire or screwdriver to make a jumper out of, you can remove the starter wire from the solenoid and touch it to the battery wire at the solenoid to make the starter spin.
If the starter tries to spin, the relay/solenoid is bad or the trigger wiring to it is not providing enough juice. If it doesn't spin you may need a new battery, a good charge, a better ground connection, or a starter.
Let us know the voltmeter readings.