i mean my system is detecting the hard disk as Seagate device ,,, but its not coming on my computer screen ... i have lots of important data in it ... i need to recover all the data ... please help me if you have a solution ...
If your HDD is detected in BIOS and shows up in Device Manager, it IS showing in Disk Management. But you may not be looking in the right place.
In Disk Management the right-hand portion has TWO panes - upper and lower - and each of them SCROLLS so you can see all they have. The Upper pane shows you all the storage devices Windows understands and can use right now. The LOWER RIGHT pane shows you those but ALSO shows you other hardware that Windows does not understand right now for some reason. That is where you should look for a "missing" drive.
Once you find it there, what does it say? For that drive there will be one large block, and on its left end will be a smaller sub-block with the disk's ID like "DISK_2", a type, a size, and a status. The main part of the block to the right will represent one or more Partitions. Each Partition also will have some information: a disk name like "BootDrive" or something, a letter name like "D:", a size in GB, a file system like "NTFS", and a status. Post here what those are.
If the "missing" unit has no letter name assigned, Windows cannot use it. In that case, RIGHT-click on the Partition and choose a letter name for it. Then back out of Disk Management and reboot to get the Registry updated.
If the "missing" unit's File System is shown as "RAW", most there is some corrupted data in the Partition Table or Directory system of the drive and Windows simply cannot understand what to do. In this case, there are data recovery tools you can get (some free, some you pay for) that will help you to recover all the files on the HDD. But to do this, you usually need a spare empty HDD because the recovery process allows you to COPY those files to a spare drive, and THEN you can repair the faulty drive once your files are safely somewhere else. (Usually a RAW drive only has corrupted data, and no actual physical flaw, so it can be repaired and re-used after you save its files somewhere.)
To deal with a RAW drive, look around the web for recovery from a RAW Format hard drive. Some software I have heard of for this includes GetDataBack for NTFS, Recuva, and EaseUS.
If you found your HDD in Disk Management and it says all of its space is Unallocated, then there is no Partition on it any more. Since you say you had a lot of data on it before, something has deleted the Partition information. However, probably the data and the file management tables are still there.
You need to do a Data Recovery operation. Just as I described in my previous post, this means using software to find and copy all your data files onto a spare empty drive. The three software packages I mentioned can do this, as well as others. Look at their websites and choose one you think can do the job well.