2 WD drives, one works, one doesnt

I have 2 WD My book external hard drives. 1 has about 800G worth of data(Drive G) and the other is brand new(Drive H). I wanted to copy the files from the first drive to the other. I plugged them both into my computer and it only recognizes drive H. When I only plug in drive G, it thinks it’s drive H and asks to format it, or it doesn’t recognize it at all. Drive G is recognized easily on my other PC. Any ideas? Thanks in advance.

Are both of these drives the same size and model?  Sometimes Windows has problems with that. If that is the problem this  http://community.wdc.com/t5/My-Passport-for-PC/Copy-files-from-one-drive-to-another/m-p/277504/highlight/false#M7587 should fix it see post 11.

Joe