This morning I planned to put new graphic card in computer. I have disconnected it from power and opened the case. Then I felt electrical discharge. IT was not strong but nevertheless scared me. I had no courage to turn computer on before I get some advice. Do I have problem with power in my house, or computer is making problems? Is it safe to turn it on?
You are obviously dealing with static electricity. It is a common thing. And dangerous for your computer but for you is safe. Humans feel static electricity discharge of more then 12000 V which can very efficiently destroy sensitive computer parts. I now that this is a big number, but as I said static electricity can not harm you. You will have to be cautious when opening computer case. Turn off power surge protector but leave it plugged in so that it will be grounded. Or buy antistatic wrist strap and wear it during work with open case. That will prevent static electricity from harming your computer and you will not feel such discharges.