About 4 weeks ago, my little sister was playing game then she saw a box which asked about the sound things. She didn't know anything then she just closed it. After that I could not hear music or any sound from my computer. I tried to install that sound program again but it was no use. Then the next day, when I click to turn on the CPU, the screen said there was NO SIGNAL. After that I can't even use my computer anymore. I thought the problems were sound card and video card but i'm not sure. IF ANYONE KNOW HOW TO FIX IT PLEASE HELP ME. THANKS.