lag help

hi usually my pc runs CA smoothly and perfectly but the last week and a half its been lagging pretty bad nd idk wat else to do ive used gamebooster nd went thru its whole system to help, made sure everythings udpated nd reinstalled game a cuple times. Now the only other problem i have w/ my pc is tht it wont install the net framework 3.5 update at all culd tht be it? either way i really need help cuz i wanna play real bad so ne help will be greatly appreciated please and thnk you