Extremely low FPS in all the games

I used to play games on my system like GTA IV, Mafia II and Counter Strike : Global Offensive around 1.5 years ago and then I quit gaming. Then after a few months, I tried playing those games again, but I started getting low FPS. Thinking of this as some software issue, I did not wanted to re-install Windows or reset my PC. I just re-installed my Graphics drivers (which failed to solve the issue).

So, today I did a full hard drive format, re-installed Windows and was shocked to see that I am still getting low FPS.

Any solutions?

System Information:
 1. Windows 10 (64-bit)
 2. Intel® Core™ i5-3337U Processor (3M Cache, up to 2.70 GHz)
 3. AMD Radeon(TM) HD 8730M with 2G DDR3 VRAM
 4. 4GB 1 DIMM (4GB x1) DDR3 1600Mhz

Reference FPS:
 1. Counter-Strike : Global Offensive
 2. Extremely Low Settings (Anti-Aliasing turned off, all details to very low, minimal resolution)
 3. Less than 20 FPS