I upgraded to Mavericks, now I cannot use my External Hard Drive

I have a 13in 2009 MacbookPro that I recently upgraded to Mavericks, and since the upgrade I am unable to mount my Toshiba External Hard Drive that prior to the upgrade worked wonderfully with this computer. The HD still works with my Windows PC. I have run Disk Utility and it appears but is greyed out and says it needs to be repaired if I try to mount it, but repairing has done nothing to help.

I need to get my HD working with my MacbookPro again. Please help me.