GE XL1800 model# jvm1851bh04 unique problem!

When I plug in my microwave, the venting fan comes on and does not turn off no matter how many times i try to turn it off from the control panel or unplug and replug. Also, I can put in times and select options but when i got to start it wont start and the fan is still on. Can anyone help with this unique problem. I was thinking fuse, but every things seems to be functions except the fan wont go off and i can use the microwave.