Before you send your genset into the shop to be repaired you can go through the basics yourself.
Start with fuel, is there enough fuel in the tank, I don't know if you are dealing with a motor home or TT installation, but, in a motor home installation the pickup tube ends about a quarter of a tank from the bottom of the tank. In other words if you have less than half a tank of fuel, go put gas in and see if the genny will run. this is one of the most common "cranks but won't start" causes I have seen for generators in RVs. The second thing you want to check is your oil level in the genny, most of them have a low oil switch that will shutdown the genny or keep it from starting when it runs low on oil. In my experience all gennys burn a little oil, so if you use it a lot, you may be low on oil. Third, check the air filter. It is usually fairly simple to check, it could be clogged, especially if you run the genny in dusty conditions. Rodents are also fond of nesting in the air intake tract.
After checking all three of those it is time to get into basic mechanical diagnostics. I could walk you through all the basics later if you can't find a shop to diagnose it. Fuel pumps are one of the most common failures, along with worn out or fouled spark plugs.
When it comes to a shop, have you tried the RV dealers around you? They have to deal with genny issues all the time.
Good luck, Dave
Dave & Kandi & Indica the Chorkie pup "Big Blue"
2001 Holiday Rambler Admiral 30D w/ 2nd slide
2000 P32 7.4 4L80E wide track J71 18/21K