https://github.com/Melvinsajith/raspberrry_Pi_Pico_windows_7_8_xp
-- "How to install Raspberry pi Pico Driver in Windows 7,8,xp"
Download the pico-serial.inf file and put it in the C:\Users\Documents and selecting that as the driver directory when the Device Manager Install Wizard popped-up worked a treat or go to computer - Manage - Device Manage and install the driver on the laptop or PC.
It seems that windows 7 requires a driver for the board(pico_w)!