After accomplishing a clean Mavericks OS installation on my MBP, I've plugged my external hard disk (HD), with USB, and it was working fine. It should be noted that, the external HDD has NTFS format. After few hours, I have updated the OS as it was requested. But now, after updating the OS, the external HD doesn't show up in the finder, desktop or disk utility. I have checked it with another laptop and found out, there is no problem with external HD.
Update: I have even installed Paragon, which allows to write on NTFS disks, but it didn't solve the problem.
How can I fix it?