Why did the computer start to slow down STRONGLY?

Question

Hard disks

The computer worked quite well, but I decided to clean it, because. windows has been installed for 2 years now. What did I do?
1. Deleted all files from the C:\Windows\Temp folder (temporary files are stored here and there were a lot of them)
2. I downloaded the everest program (checked the temperature and all parameters) - everything is ok.
3. I downloaded the crystal disk info program, here I was a little confused by ID C5 / C6, I decided not to touch them, because. the computer worked quite fast.
4. I defragmented hard drive D. Everything was fine, I turned off the computer. Today the computer began to slow down terribly, Word files could barely open. What can be wrong?

Answer 1

The IDE channel of the hard drive did not switch to PIO mode, by any chance?

Answer 2

From work under load during defragmentation, the disk died.
Copy important files and rest it.