Here are the things that I've done
> checked all the cable connectors and everything has plugged in to places
> I thought it was the power supply so I changed it because when I opened the side panel of the case and pushed the power button on, the cpu fan spins in about 2-3 secs only and turns off for about 1-2 secs and spins again and that's when i am hearing continuous beeping sound that's why I changed the PSU
> Changed the RAM from a PC that is working and still getting the same problem
> changed the cpu fan and still the same
> changed the processor but with the same speed and capacity, still the same
No external devices attached and no separate video card, so I'm suspecting it's the Mboard that is having a problem....but still not sure. what do you think?
Ok it is solved. After getting unlucky results I decided to finish with OS and to put aside 'Restart' problem for later and guess what...after updating windows everything sorted out. Still I don't get how it is possible that OS update can solve POST problem but it doesn't matter now as everything alright now. Thanks for reading guys!