Recognizing a USB hd with an os

[cwrb]

I have various hard drives (each has an OS - WinXP, Vista, Win7).When I use the WinXP hd in my laptop, i can USB connect and see the Win7 hd but not the Vista hd.
When I use the Win7 hd in my laptop, I cannot see either other USB hds.

Any idea what I can do to make the other two USB visible when running Win7?

One addn piece of info ... I partitioned the WinXP and Vista into a c-drive and d-drive but left the Win7 hd as only a c-drive.

 

[gregrocker]

Are you plugging one HD internally and placing the other in an external enclosure to connect via USB to access files?

Generally, if you cannot see another HD then you need to enter Disk Management and assign it a drive letter in the OS you are using. So if you can't see XP/Vista while booting Win7, make sure both have a drive letter assigned in Disk managment.

 

[cwrb]

Yes, i use USB enclosures.
I had checked Disk Mgmt but it didn't recognize the HDs and indicated i had to format each one. See this link.