Ubuntu 16.04 is lagging, fan is running very fast and over- heating after I changed my grub file to nomodeset!! (No dual-Boot)

Question

I have installed Ubuntu 16.04 LTS last week. First, it was booting to a black screen so I set the grub file to nomodeset. After doing this, my videos and system started lagging, sometimes more sometimes less.

I have performed following steps to improve lagging:

1. set GRUB_TIMEOUT = 0, but that didn't help me.
2. set temp_throttle to 80, that also didn't improved performance.
3. Used sudo gedit /etc/sysctl.conf and added one line to file vm.swappiness = 15 (According to one answer).

Is it something because of video drivers since I've processor AMD A4-3330MX APU with Radeon(tm) HD Graphics × 2

If my processor is too old to handle Ubuntu 16.04 LTS, then kindly suggest me the version which can run on this processor.

Laptop Specs: Laptop Specifications

Output from top in terminal: Output from top command