Why does my laptop became so laggy?

So I bought my laptop a year ago and it works fine on some games with the highest settings smoothly running like Batman Arkham City, Crysis 3, Blur, Assassin's Creed Black Flag, etc.

Then suddenly one day it slowed down and became laggy. I managed to uninstall the games and applications that I do not use anymore but it's still so slow… I also tried the recovery mode and a few weeks ago, I sent my laptop to a technician to reformat it… I got the laptop now but it still sucks and it can't even play GTA Vice City smoothly even on the lowest settings…

By the way my laptop is:

Lenovo Z470 Ideapad with dedicated video card on/off switch,
8GB RAM, Intel Core I3 - 2330M CPU @ 2.20 Ghz,
64 Bit, NVIDIA Geforce GT 540M

Guest

Well specs look alright. Then the problem might be the Dust.Dust build up is serious.It can lower performance and If the case is so bad the CPU will overheat so much that it won't even boot up.So you need to clean it.
1.shut down the laptop. 2.let it cool down 3.grab the COMPRESSED AIR CAN and blow it at the intake and exaust fans. 4.boot up the laptop download and install cpu fan and look at the temperatures. If it's 40-50C when at IDLE it's good. If it's 70-80C when IDLE that's not good you might need to chnge the thermal paste. If the temperatures are 65-75C when UNDER LOAD it's ok. If it's 90-100C that's bad.

Yakub