Is you machine still under warranty? I think there are two possibilities.
Either you got a lemon to start with or you power starved your machine by running
it on the same circuit as your iron. Of course you can run all kinds of machines
at the same time as long as they are on different circuits. I think you should
take your machine to the dealer and have it checked. Also, it might be wise
to ask your electrician to check the wiring in your house. Ask him to put
your sewing machine and iron on two different circuits.