Usb drives not recognised

Hi. Since updating to Yosemite (10.10.2) recently, my iMac 21.5" (late 2013) will not recognise any USB memory sticks or a Garmin exercise watch or their contents. I have looked at lots of posts and forums with various similar issues and followed the recommendations with no success including:

• Ensuring all Finder options are checked to recognise external drives.
• Reset the System Management Controller by powering down.
• Used direct connection and via a powered hub.
• disconnected all USB devices and then just tried the sticks one at a time as the only connected USB device.
• Tried various sticks in all ports on the mac.
• Power is getting to the ports as they charges mobile phones.
• I shut the system down daily and turn the power off and start it daily.
• Put system to sleep and woken it up.
• Restarted (in the long shot that that had a different effect to hard shut down and start).
• I use Windows (sorry) on other machines in the house and at work and the USB sticks and watch work fine on those and Pre Mavericks they worked fine on my iMac.

Any suggestions would be gratefully received.

Many thanks.