Hello.
I have an iMac 2009 21.5 with Snow Leopard. When I want logging into my System, It is very slow and take 5 minutes or more. I used some applications like "CCleaner" but not matter.
It's probably a dying hard drive 6-7 years is about the life of a well used HDD back up your computer now and look into getting the HDD replaced, an SSD replacement will make it run better than new.