"But it is a new hard drive!"
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Sorry, seen plenty of "new" drives die.
Have a look for those files I mentioned.
Also if you fan is not running to speed, your CPU will get hot, if you CPU gets too hot the machine will slow down.
If its not your fan or HDD, check your memory.
Have a look in your BIOS and see what temperature the CPU & case is running at.
Don't use an adaptor that's not the right voltage, lower or higher!
