Here's a link to your manual: http://www.managemylife.com/mmh/lis_pdf/OWNM/L1001172.pdf
No power is a result of a break in the output circuit of the generator. The most likely places for this to happen are at connection points and moving parts designed to open and close manually and automatically. These include terminal screws and push on type connectors, switches and circuit breakers.
Before beginning, you should follow the troubleshooting chart for "..No AC Output" on Page 21 of the manual.
Since there is a great deal of vibration on the entire unit, it is not unlikely to have open connections where there shouldn't be. A careful disassembly of the control box with the unit off and disconnected from the electrical panel should allow you to poke around without fear of shock or burns. It would be a good idea to take a picture or two of the connections when you open the box - before disconnecting anything. otherwise, be sure to label wires and terminals for anything you take apart.
Look for evidence of arcing or sparking. This is usually a blackened area near a terminal or wire. Clean the contact area and determine where the connection point is supposed to be and complete the circuit as per the schematic. Check for loose wires "floating" in air (aka not connected to anything). Reconnected as shown by the schematic. Next, apply pressure to all terminals and connectors to find any that are loose. Resecure any found. pay attention to those on DP1, DP2 and the 240 volt 30 amp outlet.
Using the schematic on Page 22, check the 25 Amp circuit breaker identified as CB1
by removing wires 11A and 44A from this circuit breaker's terminals. Use a multimeter set on Ohms (or resistance), set and zero to the lowest range, and test from the terminal with the #11 wire on it to the terminal that had 11A on it. With the circuit breaker ON, it should read less than a couple of Ohms. This is a closed circuit indication
. Repeat tests with terminals 44 and 44A. If you lack a meter, you should be able to use a continuity light (this will cause a light to illuminate when there is a good battery in it and there is a connection or path between the probes of the light). The meter resistance should indicate an infinite amount of resistance when the circuit breaker is turned off (as the light should go off when the circuit breaker is turned off, too). This is the open circuit indication
. If the meter never indicates a closed circuit with the breaker ON, the breaker should be replaced. If it works as expected, reconnect the 11A & 44A wires to their original terminals.
Continue to test each CB2 and CB3 the same way. Remove wire 11B from the terminal of the circuit breaker and test from wire 11A to the circuit breaker terminal that 11B was connected to. With the breaker ON, it should show as closed circuit. When off it should show open circuit. If not, replace the circuit breaker. Reconnect 11B to the circuit breaker terminal. Lastly, move to CB3 and Remove wire 44B from the terminal of the circuit breaker and test from
wire 44A to the circuit breaker terminal that 44B was connected to.
With the breaker ON, it should show as closed circuit. When off it
should show open circuit. If not, replace the circuit breaker.
Reconnect 44B to the circuit breaker terminal.
The rest of the check out requires that the generator is running and voltage measurements be taken. As little as 50 volts can kill under the right conditions, so extreme caution must be exercised. If you have never worked on these systems before or are not completely comfortable working with voltages levels this great, you should stop at this point.
Otherwise, check for the presence of 240 volts on CB1 terminal 11 & 44. If not present, there is a problem with the voltage regulator or generator windings themselves. Repairing or replacing these parts may not be worth doing depending on age of the generator, etc.
I hope this helps & good luck!