HDD problem in my MBP (early 2011)

I have an early 2011 MBP. It has a 500GB HDD, with 130GB free. I bought it new in August 2011 and its original hard drive needed to be changed last May.

Since yesterday it became VERY slow. I went to college in the morning and used it all day. When I came home, I was compiling a LaTeX file and, instead of taking the usual 5 seconds to finish, it was taking more than four minutes.

I ran the Repair Disk Permissions and Verify Disk from the Disk Utility and the situation didn't change. I installed Onyx and ran all the maintenance stuff from there and nothing change. However, it always freeze when I,m veryfying the start up disk.

I just finished the Apple Hardware Test (alt +D during boot), both regular and extended versions, and no trouble was found.

Do you have ideas for me? The computer can't be used, because I'm like just typing in it, my computer freezes and the letters show in the screen seconds later. It's so annoying.

Also, when I boot my computer, it doesn't make that boot sound.