I will work on this softwares:
Altium Designer, Proteus professional, Microsoft visual c#, MPLAB IDE, C18 Compiler, Autocad, CATIA, PRO E, Adobe Photoshop.
Please tell me suggestions what should be the configurations for my PC.
Which graphics card should i buy for the best performance?
I planned to buy i3 processor. Which motherboard should i buy?
RAM?
I think you should read this before settling on an i3.
Given what you want to run I would suggest an i7 with 16 GB of RAM 1TB HDD and a 256GB SSD with an NVIDIA graphics card as you didn't list gaming as a requirement you probably can get away with a much lower end card, but you'll definitely benefit from a card that supports at least two HD or better (i.e. 4K) resolution displays. The dual head display card will pretty much define the lowest end card you should get.
As far as I can agree with lots of RAM and definitely optical disc drives, I'd opt for getting i5 instead of i7. Definitely not i3 as it's too weak and may become not enough for you in a very short time. But i7 are very expensive on the other hand and for what you need are you guys sure that i5 wouldn't be enough?