It sounds like a problem with your computer OS, not the Blackberry. Are you using Vista or XP? Do you have a lot of other USB device? Did you remove all the 7290 drivers before you installed the 8820?

Sometimes when I've had USB problems, I go into Device Manager and delete all the USB ports, unplug all USB devices (except the KB and mouse), then reboot. After it reboots and reloads all the ports, I plug in my devices one at a time, e.g. printer, phone, GSP, etc. That usually solves any issues. Tip: Use a PS2 mouse to do this. It will keep working as you remove all the USB ports.