I have a problem with my trancend porteble hard disc.. when i connect the hard disc asq for formatted the disc.... i dont no why please tell me whats the problem.........

When Windows cannot read the "Table-Of-Contents" from a disk-drive, it takes a guess that the disk is brand-new, and requires "formatting" to make it ready to be used. Windows asks your permission, before doing that formatting.

If you have been using the drive for a while, and you have written files onto it, say 'NO'. It may be possible to "recover" those files
(like pages in a notebook -- they are not "blank", even though the Table-Of-Contents has become corrupted). Search online for "file recovery" software to read through the disk, page-by-page, that tries to reconstruct the Table-Of-Contents.

If the contents of the drive do not matter, say 'YES', to allow the formatting to occur. Take careful note whether the format completes "successfully" or "unsuccessfully".