25000+ bad sectors and counting... Yet HDD works just fine?

[Byamba]

This is LONG STORY... yet somewhat simple.

I had 2 partitions.
C - Windows 8 OS
D - Somewhat useless backup.

Windows 8 went through very weird registry and partition file error which lot of people had and have not just me, which led me to recover my files through "testdisk" by installing Ubuntu Linux on my external HDD and booting from it.

I Recovered all my files from my "C" drive, so I had to reformat my entire HDD so that I can install Windows 8 again.
So I used "DBAN" to create a boot disk and completely wipeout my HDD. The process didn't go very smooth, I mean it was just hard to tell what was happening it took over night and my HDD was making noises, so the morning I woke up I did a quick format.

Then I put my Windows 8 disk and installed it on my HDD. It was all unallocated space, no partitions, no nothing, so I had to create a new partition and install Windows 8. Windows 8 installation did say my hard disk may fail, well I installed it anyways.

NOw I am on Windows 8, it run just fine, not lagging or anything, infact faster than before I think. I still believed the bad sectors and the errors were on my HDD so I used "HDD REGENERATOR" to create boot disk and check my drive.

The process said it would take nearly 3 days to finish. It found 25000+ and STILL counting bad sectors so I knew it was going to take forever considering my HDD is 500gb, so I just quit. I used windows 8 disk check, shows no problems.

I am very confused??? My HDD seems to function just fine, but the way it is recognized by some programs, they say it is really bad because of many bad sectors so it may fail soon.
I don't think this is a physical sector, my computer stays where it is, I don't do anything to it. The Windows 8 Recovery partition became corrupt resulting in not allowing a fresh installation, and messed up my C drive, so I formatted and its functional but thousands of bad sectors.

What is this? and how do I fix it?

[Byamba]

I just used chdkdsk /f from boot and it scanned and the process finished quite fast so I think it didn't find anything bad.

DBAN did some weird stuffs to my HDD, but that was perhaps the ONLY way I could completely format my entire HDD.
Formatting through Linux Ubuntu gave me errors.

[dobrevjetser]

Check the smart of your harddisk and put the result here.
This can tell us a lot about what is going on.

[BlackST]

... What is this? and how do I fix it?

Simply the disk is worn out and there's nothing you can do at home without expensive tools. Replace it.
Plan B : contact a pro in your area who knows what to do and has the right gear (NO you can't download from the internet, it's HW tools) and is willing to try to fix the disk for a nominal fee.

I do it routinely as job, but I'm too far and also Ihave a feeling the disk is excessively worn out if the count is real (maybe there is another problem, but only having the disk at hand I can tell).