About VGA card

i would like to ask , when i playing games my computer will suddenly blackout i will need to close the screen for about 1 min than open back it will be back to normal but it will keep repeating the same thing , i ask some of my friend's they say is the VGA card spoit but it works fine when i was just using internet , i just update [ MS-7525 Motherboard BIOS Update ] from the hp website [Enhancements •Improves compatibility with Nvidia GeForce G210 graphics card. •Resolves issue with system hanging at HP logo during startup. •Improves BIOS security. •Updates processor thermal policy. ] but it repeat the same thing again . any opinion about this ? cause i wanna fix it ASAP .

Could be one of a couple of things, either the game(s) are that high a spec the card is struggling to do it's job, or the more likely culprit is the temperature, try running Speedfan and Motherboard Monitor, see what they report as the system temp's, they are not always correct in they're reports, but they will help to see if this may be an issue, a quick test to try is to remove the side of the case, then place a fan pointing into it so it moves more air, if it is a temp's problem doing this should make things more stable.
Also when was the last time you cleaned the dust out of your case ?

how to on speedfan and the motherboard monitor ? than i should buy a small fan facing where ? monitor or cpu ? i think i never clean my dust before but i did normal one like cleaning the monitor , keyboard and some dust on the cpu that i can see not really go and open the whole casing and clean really throughly but the dust may cause some of the problems ? so i should open the casing and clean it or ?

If you aren't comfortable with opening the case, then take it to a repairs shop. Either way, keeping the inside of the tower clean is important, and should be done regularly. This may very well be causing the problems.