Tips on upgrading my gaming computer?And Resolving CPU Shut Off Issue?

[iggybug]

Hello,
I have a desktop PC which I use for gaming. I would like to upgrade the system as the computer would sometimes crash in the middle of a video game (black screen, CPU turn off, monitor LCD blinking, sometimes with stuck noises of game from speakers). I have asked the store about this and they said that it's probably a problem with the PSU. I changed it but the problem persists. This is my system information:
Microsoft Windows 7 Ultimate
Intel Core 2 Quad Q9400 @ 2.66 GHz
NVIDIA GeForce 9600 GT 512MB
4 GB RAM DDR2
Motherboard: Gigabyte EP45-DS3

If anyone would help, I would greatly appreciate it. I will provide any further information if needed.

EDIT:
I have 4 GB RAM, not 2 GB.

 

[drew455]

you need more Ram. at least 4GB. and that video card will limit your settings.

 

[Star72]

Also, you said you changed your PSU. What did you change it to?

 

[singemagique]

To improve gaming I would focus on getting a better GPU, more RAM, and a SSD. Your CPU is new enough not to be much of a bottleneck for gaming.

I would bump up the RAM to at least 4GB, maybe even 8GB if you have extra cash. Something like this would be fine: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231122

As for the GPU, I'm not sure what type of games you play, but if you want to play the most current (ie. BF3, Arkham City) I would get at least a GTX 570: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231122

And for an SSD all you really need is something large enough to hold the OS and the major games you play (ie 64 - 128GB). I prefer Intel SSDs, but OCZ also makes decent quality drives such as:
Intel 320: http://www.newegg.com/Product/Product.aspx?Item=N82E16820167050
OCZ Vertex 3: http://www.newegg.com/Product/Product.aspx?Item=N82E16820227706

The shutting off of the computer could be due to a number of things, such as overheating (for this you could try reseating the CPU HSF with some new thermal compound (ie. Arctic Silver 5)) and also do check the PSU. Is it high quality and providing enough watts to meet the demands of the system.

 

[iggybug]

Well, this is a bit weird, I remembered that when I first bought the computer, I had 4 GB RAM, and after I installed 64 bit Win 7, sometimes it would just show 3/3.something GB. But now only 2 GB is shown. Is something wrong?

Between, I'm not sure which PSU I had before and now. Is there a way to check it up without removing the case?

And, what is an SSD and how does it affect my system/gaming?

I'm still not sure what causes the computer shut offs. Is there a way to determine it? My computer is self built by a shop, but when I sent it back they can't seem to find the problem. Sending it to other shops would just waste my money as one changed my PSU with no difference.

And I almost forgot, the CPU also seem to produce stuck noises as well everytime it shuts off.

 

[iggybug]

bump. please help