Have you tryed this
Reset the PRAM > http://support.apple.com/kb/HT1379
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.
Have you tried resetting the SMC which is the System Management Controller?
I think it used to be called the PMU Power Management Unit on older laptops.
Anyway a link for you to follow with instructions:
I have had a similar problem since upgrading to Lion 10.7.3. I have a MacPro and all was going well. However, now I have huge problems with my USB ports. Some are recognized some of the time if I unplug then replug, but not in a reliable manner. This applies to USB ports at both the front and back of my computer. My printer won't work or my mouse won't work (but at times I can get one or the other), but any external USB drives (including camera's) and my iPhone are not recognized. Obviously very frustrating. Other issues that seem to have occured are recognition of Outlook for Mac, so have reverted to MacMail (not as good, but working).
Looking through a variety of threads, this issue isn't that new going back to at least July of 2011 (http://www.mac-forums.com/forums/os-x-operating-system/245665-os-x-lion-will-not -read-external-hard-drives-usb-flash-drives.html).
I am also involved in long-running saga with "upgrade" from MobileMe to iCloud that has led to many individuals (including myself) losing "push" email capability despite 9 months and 35 pages worth of problems on the Apple Support site (https://discussions.apple.com/message/18033340?ac_cid=142432#18033340).
Having been an Apple user since 1988 it is ironic that as it becomes more popular it becomes increasingly less reliable.
Does anyone have any solutions for the USB problem that are reliable?
Had the same problem on a brand new 2012 MacBook Pro 15 inch, Model : MacBookPro8,2.
After a couple of weeks the 2nd USB port would not work at all, just died one day for no reason I could tell, the only thing I ever plugged into it was Apple products, the 1st USB port worked fine. Tried all the above suggestions, nothing worked. The diagnostic About This Mac, More Info..., Hardware USB would never show anything connected to this port. Remember you have to restart this diagnostic everytime you plug something into it.
Then I decided it had to be a stored value in some memory location that needed to be reset, and the only way to do that was to disconnect the laptop's battery so this memory would be reset. Therefore I had to open the MacBook Pro back cover, unscrew the 10 phillips screws with a #1 phillips screw driver, and just disconnected the battery connector, and let it sit like that for a minute. Then plugged in the battery connector, reassembled the back cover, turned it on, and the 2nd USB port now works fine.
Apple should have some software diagnostic tool to do this for you, but if all else fails you can do what I did. If this doesn't work, then it's likely a hardware problem on the USB port, but that would be a very rare circumstance. The USB ports are protected electrically with bypass diodes to make sure they don't get damaged by a peripheral drawing too much power or some other electrical problem.
Hope this helps someone...
I ended up going to the apple store about an hour and a half away from me. They dusted my mac and ran some tests. Everything seemed fine surprisingly (I felt like an idiot seeing as they found nothing wrong with it) and the ports were up and running mostly, except that my nearest port was drawing a little less power.
No less than 24 hours upon returning back did they stop working again.
It might have to do with something involving the download of iCloud or something? ^ or the new lion, both of which I am not sure of.
Just solved a similar problem:
A couple of days after installing the 10.7.4 update on a MacPro (4core, 14G RAM, early 2009) 3 of 5 USB ports stopped working. PRAM, SMC reset did not help.
I rebooted from ext. disk into Snow Leopard - all ports OK.
Reboot in Lion 10.7.4. - all ports working - for now.
Hope that helps someone.