Sambarta Banerjee :
Ohh another thing!!
If I am planning to upgrade my pc to intel i7 4790K or AMD FX 8350.Then can you suggest me a good motherboard,RAM,PSU for both?
if you already have a i3 2120, then the same motherboard you have can be upgraded to the i5 2400, i5 2500, or i7 2600. As well as the "k" variants.
Which are all better then the 8350.
The i7 2600 is still very powerful.
You should also have the proper ddr3 ram, just make sure to get 8gb total.
All you need is a good 500w power supply.
Choose from this list, tier 1 or 2 unit in 500w or better:
http://www.tomshardware.co.uk/forum/id-2547993/psu-tier-list.html