SimpleTech 500gb external hard drive not recognized

Hello, after upgrading to Maverics, my external HD was no longer recognized. I can't see it at all, not even in disk utility. The simple tech website is not very good, or maybe it's me, but I couldn't find anything as far as troubleshooting for OS X there at all.

Not sure where to go next and I know there are a lot of people smarter than me reading these threads, so I will say thank you in advance for any suggestions.

THANKS!