iMac mid 2010 running slow [Specs of the iMac, the iMac already have 8GB(Should be enough to handle Yosemite)]
[1]http://www.everymac.com/systems/apple/imac/specs/imac-core-i3-3.2-21-inch-aluminum-mid-2010-specs.html#macspecs1

Yesterday i bought this iMac, it's took around 45mins to boot up and it's unusable due to the slow response. Each click takes around 15mins to response. So i done a clean installation of yosemite and updated to the latest version. And it's now become normal(boot up around 3mins) except the temperature is high at around 110C. I open up the iMac and clean the dust inside(All three fan) but it's still running at around 100C. 

But, when i try to copy VLC from the dmg, it's become slow again suddenly, though the boot up time didn't reach 45mins, but the OS become so laggy. I did not install any software except iStatMenus Trial and the VLC.

Any idea what is failing in this iMac?Could it be the HDD?
One more question, does putting on new thermal paste help cool down the iMac?
In the end, i send it to some expert to check on it.
There is two reason the machine is slow:
1. KVR ram is used for the machine
2. The HDD is most probably faulty.

Swap this two things out it worked fine.