Anyways I just bought a new laptop using windows 7 and 64 bit, and also had issues with staying connected. I loaded 4 different versions of drivers for my prolific cable. Well after hours I finally found one driver that worked and Procede stayed connected. Here is the link
http://www.serialgear.com/USB-Serial...-mac-linux.cfm
Might sound crazy but it might work for you...Uninstall the usb serial driver and upload this one...