External hard disk is not recognised by xp

Hello,

i was using my laptop lod hard disc as external hard disc with toshiba cover case. before it was working normally but after formatting it is not recognised by window xp.

Exteran hard disc Brand is western digital
it is serial ATA hard drive
i m using with toshiba2.0 cover case

if anybody can help me i will be thankfull to him

panchiwala