All USB devices stop responding after a few minutes of capturing video from multiple webcams

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http://stackoverflow.com – I am using v4l4j, which is a java library that interfaces with v4l, to acquire frames from usb webcams. I have three stereo webcams (for a total of six cameras /dev/video0-6). They are connected directly to the computer via 3 USB 2.0 cables. The problem is whenever I try to capture from more than one device (2 cameras) at a time, all of the USB ports on my computer (including the ones the cameras weren't plugged into) will stop responding after a minute of capturing or so. They don't even appear when I do lsusb. The only way to get them working again is to reboot. (HowTos)