I need to control my PC with an IR remote control.
The piece of software I think I can use is WinLIRC. Or can someone can suggest something else?
Please can someone give me the simplest hardware design for an IR-Receiver?
The IR receiver is trivial - you just buy one of the three-terminal IR receiver modules, which will give you a nice clean set of pulses. (for example, search for GP1U on Digikey)
Getting the pulses into the PC is harder, and if you're planning to use someone else's software to decode them (e.g. WinLIRC), then you should follow their recommendations - the WinLIRC site has a page of stuff about this. If I was doing this from scratch, I'd probably decode it all in a micro and send something higher-level up a USB cable - perhaps pretend to be a HID keyboard, but that's quite a lot to get going if you haven't done something like that before.
In real life, I wouldn't develop anything like this, as it's a tedious commodity building-block, which has already been done a million times - I'd go here: Google search.
and buy something someone has already made.
You can build one from the official LIRC instructions.
You could also very easily hook up an Arduino, Mini, Nano, Pro Mini, or Micro with a simple receiver and library. It will communicate via serial (over USB) to WinLIRC on your computer.