ok im trying to use my old laptop hdd as a external hdd whit an enclosure (2.5 sata and ide to usb2.0 imicro)so when i conect the hdd via usb my hpmini recognize the hdd but i cant see him in my computer or disk management, i had window xp in that hdd ...or i still have i dont know.i tryd to format it whit easeus and minitool partition but i get error oh and i can see him there as a unallocated

Make sure that the HD is formatted and partitioned in a file-system your OS can read.
If you are using windows try Disk Management.

In disk management ->
there will be your system HD and your external HD.
Try to allocate a partition if unallocated, on your external HD.
Format it : filesystem can be either NTFS or FAT32. (FAT32 is faster but has a limitation that it cannot store a file greater than 4 GB)

Now, I hope it appears in my computer.

You just check your usb driver, in which port you attach your hard disk this port is not working .Install proper driver. Other wise your hard disk may have corrupted. Consult with hardware specialist.