I also have problems with this WD 500gig external HD using the eSata port in Windows7 x64 Ulitimate. I have a pci-e silicon esata card in a Dell GX620 Pentium D 3.6. I have another enclosure using a XTRASTOR brand which seems to work OK in Windows7. It has to be the WD external HD. It has to boot for it to work, otherwise it freezes. I have WinXP pro and Win7 on a dual boot. I did have some problems with one eSata cable that seems to be a little fidgety but only in Win7. I like this dual booting XP and Win7 x64. It gives you time to work out problems. So far I continue to hate the design of Vista/Win7 and oddities like this does'nt make me like it more. I doubt I'll use Win7 for along time on a regular basis. I have yet to see any good reason. I like WinXP.