Usb com ports disappear

I have a sony erricson w600i , the laptop is a hp dv8130 (amd64/w ati chipset). If I have just started the computer up and tether the phone it works fine. But if I have to answer a call or unhook it, my com port dissappears. No amount of mucking around brings it back. funny thing is, the laptop will still see the phone as storage device. I have noticed the same thing with my usbto serial connector too, it will lose com ports, but once I reboot they come back. I have used this phone on my other laptop and have never had an issue with it. This happens in both xp media center and vista. It even does the same thing when using the usb ports on pccard. I have all the newest updates for the laptop and the phone..