USB flash drives not showing up in Disk Utility

My 2013 iMac w/Mavericks refuses to see any USB flash drive I attach. These drives are all mounted just fine on my MacBook running Lion.

I have an external DVD drive that DOES mount on my iMac. What the heck? This is making it extremely difficulty to install Windows 8!!!! Argh!

Little help?

Thanks!

Fixed it! CyberSecurity for Mac was blocking attached media devices.