You did say 'Powered hubs' That is to say plugged to the mains to make them indipendant of the Machines power supply.
As JT says plugging Unpowered hubs into a lappie could 'pull' the power down to such a level that a machine will not function. But Powered? I wonder if there is not some form of feed back here. Check out with the Makers Web site or Support line.
Hi, if you had only bought one powered hub, I would have suggested a dodgy hub, but probably not two - in which case I would suspect a dodgy usb port in laptop; or does any other usb peripheral work when plugged directly into laptop?
other devices are working OK when plugged into the laptop usb port.
I have heard of problems with usb connectors not being able to get fully into laptop ports because of their design - is it possible this may be happening with both hubs or are you sure the plugs are going in fully - perhaps try a usb extension cable before the hub?