Transfer speed slow down

i have a problem when copying file from/to same partition (WD Blue-wd10jpcx). first, the transfer speed is about 78 MB/s, but after few seconds it goes slow down to 20 MB/s. Before, transfer speed was normal and stable 78-80 MB/s. I had checked health of my internal hdd, it said good with no error found. So, what can i do to solve this problem?

Hello there,

Have you changed anything on the computer or the operating system before this started happening?

Yes, i had changed internal hdd with my old hdd from my notebook that ran win xp. I did it because i want to access my old file from my old hdd. when i turned on, win xp logo was showing up then it showed bsod. So, i returned hdd (WD Blue) back. I turned on my laptop, win 10 logo was showing up then it showed bsod. So my laptop restarted automatically.
Now when i try to copying file, transfer speed will be slow down after a few seconds.
i make sure that my WD-Blue has connected correctly