Sounds tho it's getting to one of:
=> A faulty device (e.g. the printer itself)
=> A faulty hub or
=> Faulty USB ports
Have you tested without using any hubs??? (plug the printer directly into computer USB port)
=> Don't attach ANY external hubs
=> Test printer on EACH computer usb port
=> Are you mouse/keyboard USB? While i would guess they're not the problem source, would be best if you could attach them using non-USB ports to be certain (e.g. get a USB-PS/2 adapter, if you have PS/2 ports, for the connector runs about $2-3 USD)
Also, Open Device Manager, look at each hub under USB
Rt click Properties->Power. You'll the each USB device listed AND the amount of power drawn by each device and total power usage. Anything interesting in the Power info for each usb hub on your computer (when reporting tell us info and if hub says Generic Hub or Root Hub)