Ok this could take a while, so i'm going to skip over a few steps that I do as a repairman, so I don't have to write a book here.
You wont need any special testing equipment this way either.
1. Make sure the wire hasn't come loose from the timer.
2. Turn on station 1 at the timer. Now go out to the valve. It's probably the same color wire that's attached to the timer.
3. Make sure the wires haven't come loose at the valve.
4. Try turning the valve on manually by opening a bleeder screw or by turning the solenoid. If it wont come on then it's the valve itself. Even if it comes on it could still be the valve.
5. With the power on to wire number 1 hook it up to another valve and see if it comes on. If it does the wire's ok and you know it's the valve. If it doesn't come on then the wire's been cut somewhere along the line. Look around, maybe the gardener cut it. There's also a slim possiblity that the timer itself isn't putting out a signal. You could move wire number 2 to the number 1 terminal and turn it on.
The valve should come on.
Basically it's either the timer not putting out power. The wire being cut somewhere between the timer and the valve. The valve itself.
Most valves are easy to repair. Sometimes it's just as easy to change the valve. If you get stuck or need help fixing the valve come on back. Bring the valve name and model number if you can. Or a description will probably do.
If I can't fix it, it's broken!
