When i am playing games my screen turns black

[jpotocn]

Hello,My name is Jan and i will describe my problem,first i apologize for my bad english.So im using my computer for over 3 years now and it has some problems.When i installed Mafia 2 game(that is when i was using my computer first time,that was 30.8.2010 I remember date because it was school next day )and played it it was been fine,no errors,nothing,everything went cool.So i decided to install another game,so i installed Medal Of honor 2010 Multiplayer BETA.When i played this game from start everything was cool,gameplay good and so on but in the middle of playing computer freez with some green/white dots I don't know and monitor went off BUT the speaker wass still on and it was noise comming out for 15 seconds then the noise becomes all messed up.So I was like oh its nothing its 2 month using my computer,nothing personal,but these problems was repeating all ofer again with some other games like crysis 2,crysis 1,assassin's creed 1,...I didn't test nothing because i can not...So I have these problems now and i really asking you to help me solve problems i will really appreciate you for helping me and for response.Thank you.

Some other games like skyrim,hitman absolution are working perfect so these problems are happening with a lot of my games this games are exceptions.

My Specs:
-CPU:Amd Athlon II X4 645
-Motherboard:MSI-760GM-E51
-Graphics Card:Nvidia Geforce GTS 250 1GB
-RAM 4GB
-PSU:LC Power(i can't remember numbers.. )650W

 

[lostgamer_03]

It sounds like overheating to me, it's a fairly old Card. You might consider to upgrade?

 

[odiervr]

My guesses:

1. Bad, dying, or overheating Graphics Card
- try to reseat it (take it out,put it back in). probably won't help, but it could.
- do you have access to another card to troubleshoot the problem?

That's my guess.

2.