External USB Drive Unknown and Not Initialized

Hello to All,


I have a 500 GB external USB drive that I can't access on my wife's Windows 8.1 laptop. I have confirmed that is in good operating condition on my XP PC where I can access all my files but in Computer Management on the Windows 8.1 laptop it displays as Disk 1 with a red arrow pointing down and it says Unknown and Not Initialized. Can someone help?
Thanks


Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8.1, 64 bit
Processor: Intel(R) Core(TM) i7-4500U CPU @ 1.80GHz, Intel64 Family 6 Model 69 Stepping 1
Processor Count: 4
RAM: 7908 Mb
Graphics Card: Intel(R) HD Graphics Family, -1984 Mb
Hard Drives: C: Total - 940362 MB, Free - 902392 MB;
Motherboard: Dell Inc., Inspiron 5537
Antivirus: McAfee Anti-Virus and Anti-Spyware, Updated and Enabled