Start by moving your cable modem to Ethernet. It sounds like you're saying it has both types of connections available? I'm crossing my fingers that you don't have both the modem's USB and Ethernet ports connected at the same time.
You say you get many "unplug hardware" alerts. Do you mean the "you disconnected a USB device improperly" alert? That's bad and nothing to do with your cable internet service. Could be a physical cabling/wire/plug problem though.
I count 4 devices and you said 4 ports total. Do you just have one device plugged per computer port or is there an external hub?
Doesn't sound like you have any High Power devices connected that would overload the 500mA limit but I'd still try fewer devices & see how it works. Gets us back to moving the cable modem to Ethernet. It's a better connection method anyway, especially since you mostly likely are using USB 1.1 (12Mb bandwidth). Give it a try and let us know how it goes.