As it says in the title, if I plug the USB in my arduino nano it isn't recognized by the computer, but if I power it through the VIN pin it turns on normaly. It turns ons the POWER led but it is very dim. The arduino started doing that after it smoked a little.
If it smoked its done and a valuable lesson learned !
Now you need to work out WHY it smoked and avoid doing that in future.
9 times from 10 the user abused something to make it smoke.