From the menu bar, select
▹ System Preferences ▹ Energy Saver ▹ Power Adapter
and uncheck the box labeled Put the hard disk(s) to sleep when possible, if it's checked.
If the drive has more than one interface (USB, FireWire, Thunderbolt, eSATA), try one of the other interfaces.
Check that the data cable is securely inserted at both ends.
Try a different cable.
If you're connecting the drive through a hub, connect it directly to a built-in port on the Mac.
If you're connecting it directly, try a different port.
Disconnect all other devices on the bus, or as many as possible.
Test the drive with another Mac. Test another drive with this Mac.
If the drive is bus-powered, but has an AC adapter, connect the adapter.
Start up in Recovery mode and launch Disk Utility. Is the drive recognized?
Start up in Safe Mode and test.
If the drive doesn't work under any of the above conditions, and if another drive does work with the same Mac, then the drive has failed. You may be able to salvage the mechanism by removing it from the enclosure and installing it in another one, or in a drive dock.
I think the issue is purely down to OS. I was able to use that drive with version 10.9.2. I encounter the above-mentioned issue once after I upgrade my OS to 10.9.3.
Is there any known issue regarding OS 10.9.3 with external hard drive (Seagate GoFlex Portable).
Thank you for your kind help.
Here are what I have done so far with no avail.
1) uncheck the Put the hard disk(s) to sleep when possible...Not working
2) Tried different port...Not working
3) Tested the troubled drive with different mac (osx 10.6)...OK
4) Test different drive (but NTFS formatted drive) ...Able to read and write...using Seagate app.
5) Boot in safe mode, but the drive was not found in Disk Utility.
6) Reset NVRM...Not working
7) Reset SMC...Not working
the only thing i didn't do so far is recovery test, as I don't have any back up drive to back up my present data.
I am thinking of re-formatting the drive in osx 10.6 and test again.