It would seem that the USB ports on my 2009 quad 2.66 i5 27" iMac are dying. External drives plugged into them only show up in Disk Utility for a split second, forcing me to plug them into a hub. This forces them to mount, but the connection intermittently dies and comes back to life before the disks dismount, causing missing disk errors in applications and causing my keyboard and mouse to miss keystrokes and clicks. I'm running Mountain Lion final. This is definitely a hardware issue; booting into a different OS doesn't help. What can I do, short of paying for a several-hundred-dollar motherboard replacement? I never bought AppleCare and had the motherboard replaced once during its original 1-year warranty.