Likely a fuel pump problem, especially if intermittent. However, check the fuel filter. If the bike has been sitting for a length of time with water in the fuel, the water will cause the filter to start to disentigrate. This in turn clogs or blocks the injector.
The best way to test is to remove the injector, and while it's still attached to the harness, attempt to start the bike. You should get a powerful, even spray of fuel. If the spray pattern is uneven it indicates a clogged injector. If it just sort of dribbles out, or there is no spray at all, that's a bad fuel pump.
Do you have spark at the plug? I don't know if the 125 is a coil on plug or separate coil, but either way remove the plug from the motor and ground it against the case, with the wire/coil still attached. Try and start the bike. Do you get white, hot spark?
Actually, before you do any of that get some ether and spray it in the intake while you're trying to start it. If the bike runs on ether your problem is fuel-system related. If it doesn't, it is likely spark-related. I'd look at that side stand switch to make sure it's operating correctly.