Solved Windows 8 doesn't recognize my old partition

Hello
I've decidede to upgrade my girlfriend's computer from Vista to Windows 8.
I didn't dare to delete the old O.S, thus I installed it on a different hard disk. (*)

Now I can choose to boot from Vista or WIndows 8. Both work.
From Vista everything is OK. It recognizes his partition and W8's one as well.
But from Windows 8 I cannot acces the old Vista partition in the other disk (ntfs too). It says that is unallocated.
What can I do?
I don't think I have to repair the partition because it's working well if I boot from Vista.
With other tools such as easeus it's the same. From Linux everything is OK.
Regards





(*) In fact it's in an external disk, but it boots properly and everything seems OK, except the partition issue.

I've seen that other user had this issue too. But he had too many partitions. I hust have two primary partitions on each disk.

OK, I've found the solution myself.
I don't know why Windows Disk Manager didn't allow me to do anything.
But using a third party disk management application I assigned a drive letter to the partition and now it works.