"No signal "keeps popping up on my computer?

i'l be playing a game and this only happens when im playing the game and the monitor just goes blank and "no signal" pops up. i checked all the wires everythings plugged in correctly and i even unplugged the entire computer and held the power button for a minute (said to do that in another thread) and t still doesnt work, ugh seriously ts so frustrating! i have a windws 7 PLEASE HELP like no joke :(