new hard drive Continuously above 90 procent

Hey everyone,

I installed a new hard drive in my laptop. I want to sell the laptop, old hard drive was broken.

I ordered a new hard drive ( 320 gb HDD sata , 8mb cache , 7200 RPM) , did a clean install of win 7 ( than upgraded to win 10 , installed al the drivers... and software.. )

now when i start the laptop , it starts fast enough, but once in windows it is very slow ( core i3 processor and 8 gb of ram) .

when i check the performance i see that the hard drive is Continuously above 90 procent.. ( and even most of the time at 100 procent) but i don't see anything abnormal.

he is writing to a system service but only 0.3 mb/s .. sometimes when i open firefox he is writing 3.3 mb/s .. but thats the highest that i saw...

Even when the performance is dropping to lower than 50 procent, it is jumping up and down from lower than 50 procent to 90 or 95 procent , dropping again , back to 95 procent... well you see how this is going...

I alrady disabled a lot of start up services and programs.. but even after one hour after starting up he is jumping up and down... see picture

anyone a solution?

i want to sell the laptop, but only when is is acting on a normal level...

tnaks in advance