I have a macbook air that is around 8 months old. I have noticed recently that the USB port only seems to work with devices that have their own power source (eg cameras and printers), but that if I connect to eg my external disk drive, or a USB memory stick, there is no response. To be clear, the disk drive won't even accept a disk (presumably through lack of power) and neither of these devices can be recognised in Finder.
Any ideas/suggestions appreciated.
Try to Reset Your PRAM. Do it without any USB connections. Hopefully this should help.
Mac Pro Dual 2.8 Quad (2nd gen), 14G Ram, Two DVD-RW Drives, OS X 10.8.3
2006 Mac Book Pro 2.16 (first Gen) OS X 10.7.4
2TB Time Capsule, 2 TB
32G iPhone 4S Black, iPad (3rd Gen) 32G Black