System is busy waiting for the close program ... et al

I have a Dell Inspiron 4000 on which the USB broke. I then bought an PC USB card which worked for several months fine. Maybe it still does - I can still use it to download photos from my Cannon camera, however .. when I try to us my Yamaha CD burner the whole system freezes and I get the above "The system is busy waiting for the close program" message and then even that freezes. If I try to download from a new Olympus camera it says something about a fault in the system and freezes. If I try to use my scanner nothing whatsoever happens, its as if I hadn't plugged it in. THEN when I try to disconnect whatever the appliance is and use the icon in the taskbar it says it is not possible to disconnect the item. It never is possible and if I turn off the computer (or it does it for me by freezing) I get an admonishing message about how I might damage my computer by not using the icon. Long message - sorry - any ideas?