Several Files on an Internal Drive are freezing when I try to use, copy or move them.

Various Files in different directories on my larger 1.5 TB drive over the course of a couple days, all of a sudden have become unusable. Some of them are PSDs, others are zips, FLAs, and other work files that I use frequently. When I attempt to open a problematic PSD file, it will open Photoshop, but then freeze. To the point in which even ending the process won't effect it. Copying and trying to move a file also freezes explorer. Canceling out of the process freezes the process window.

When I try to back up the file onto an external hard drive, it freezes the backup program (Goodsync), and once again makes it impossible for it to close... even using Task manager's process ender.

This is very worrying. I'm not even sure the extent of problematic files on this drive. They seem to have happened randomly to different files everywhere in this drive.

I have already defragmented the drive. Problems continue.

I'm not sure how to solve it. Would deeply appreciate any advice that can be given. Thanks!

My Specs:
Processor: Intel Core 2 Quad Q6600 2.4GHz (1066MHz FSB) (8MB Cache)
Motherboard: nVidia 680i LT Core 2 Quad (By: eVGA) (nForce 680i SLI) (A1 Revision)
RAM: 8GB OCZ OCZ2RPR10664GK
Video: XFX HD-487A-ZWFC Radeon HD 4870 1GB 256-bit GDDR5
OS: Windows 7 64-bit