normally when you connect your phone to PC, you'd be presented with choices to either connect using mass storage mode or PC suite mode. selecting area outside this dialog will set the phone on neither one, simply leave you at charging mode

or you could try force it to PC suite mode using PC-Connectivity Manager
http://maemo.org/packages/view/pc-connectivity-manager/

edit. ah sorry, just reread your question and apparently you can select them on your phone but still not detected on the PC side, right?
have you tried looking at the device manager and uninstall existing driver and let the device reinstall the next time it's connected?