USB device is not recognized some times

I own a w600i Sony Ericsson cell phone and connect it to my computer so I can access the picures taken with the phone.  The problem is my laptop only recognizes the phone the first time I connect it with the USB cable.  If I disconnect and reconnect, the computer does nothing and I get a message on the software that came with the phone that no device is connected and for it to work I have to reboot my computer.   Also, after having used the phone and tried to reconnect but fail, when I shut down the computer I get a message saying mim.exe is not responding.  I guess this has something to do with this because it only happens when connecting the phone.  Let me know where the problem is so the phone is always recognized.