I just bought a mishto 220amp 3 in 1 welder, didn't come with user manual!@!.. the arc (mma) works fine but can not get the mig working.

connect the + lead to the spool gun so that there is power at the end of the wire to make the arc
there should have been a user manual showing how to connect it into the system
try searching -- user manual for ( make and model of ) spool gun

Nevada MIG-220BZ MIG TIG MMA ARC DC Inverter Welder ...

www.ebay.com.au > Industrial > Welding > Welders

eBayNevada MIG-220BZ MIG TIG MMA ARC DC Inverter Welder Welding ... Nevada Welding machine; MIG Torch; Earth Clamp; Electrode Holder; Safety Mask ..

Never heard of anything like that.

The Rossi 220bz mig welder comes set up to use gas welding, that is with the Mig electrode connected to the positive terminal, inside the machine.
To use gasless mig wleding, the mig wire must be disconnected from the positive terminal inside the machine and reconnected to the Negative terminal - inside the machine. Open both the side coveres of the welder using a phillips screwdriver. Use a 13mm spanner to undo the hex nut holding the thick copper Mig lead to the terminal named positive, then lead it through the machine to the terminal on the oppisite side of the machine, labelled negative and screw it in place there with a 13mm hex screw. Be carefull not to bump any of the many electric parts inside the machine.
If you run the Mig welder in gasless mode with positive earth and positive elecrode it will blow the household electric fuse.
If you run the Mig welder in gasless mode with negative earth and positive electrode it will work, but the end of the Mig gun tip will get very very hot and start smoking abnormally from excessive heat.
But if you take the side covers off and rewire it (takes about 10 minutes) to negative Mig Electrode, the Mig gun tip remains cool and does not overheat. You will have to cut just one white cable tie, to get an extra inch or so of free Mig cable, so the thick copper Mig lead will reach accross to the terminal on the other side of the machine named negative. Stick the earth lead at the front in the positive terminal.
I did this on my Rossi 220bz mig welder.
http://www.weldequip.com/gasless-mig-wire.htm

Follow this Link:
http://www.clarkeservice.co.uk/manuals/mig_welders/migpro90_150te.pdf

Let us know if it was the right one.

Internal fuse inline with the transformer output to the gun.

There is a small chance the transformer burned out, but more likely the switch has dirty contacts or burned out. If you turn the switch through all heat positions 2 or 3 times before you start welding in the morning, it should remedy it in the future. In the short term, spray some contact cleaner (or even WD 40 in this rare instance) into the heat selector switch and rotate it through the ranges a number of times to remove corrosion from contacts.

Will the wire arc when dragged across the ground clamp? If not- there are internal fuses in the machine and they may be loose or blown. There should be one in series with the "hot side" (the gun) of the circuit and sometimes on the ground clamp side of the circuit.

There is a small chance the transformer burned out, but more likely the switch has severely corroded or dirty contacts or the switch burned out.

Do you have nozzle on properly, The gas flowing out the end? Your gas flow should be about 8 to 12 psi. Check your wire speed. Sounds like You have too much wire speed. Make sure the ground cable is tight. Did you reverse the polarity when you went from flux wire to hard wire? Is your wire er70s-6? This is the wire you want for mild steel. Without seeing your setup and knowing what you are trying to weld leaves too many varables.If it is a newer machine, try taking back to where you purchased it or to a dealer who has that make & model

Sounds like the trigger is getting worn out.