Please Help!!

Okay guys, a new problem...My RAM seems to be acting up now...Here's the situation...I am guessing something is up here...:
Slot 1: 256MB PC3200 RAM
Slot 2: 256MB PC2700 RAM
Slot 3: 512MB PC3200 RAM
Slot 4: Nothing...
I am guessing there is something with that odd 2700 in there...As a result, whenever I run a game...say like NFSMW, I can access it for a while...and then I get a black screen...My machine stay's on...the only way to stop this is to manually reboot (press and hold Power button)...Funnily enough, this does NOT happen with FS9...I thought this was a PSU issue first, but it turns out it's not...
Also, this problem has never effected the system other than the time I play any games (except FS9)...
So, I was thinking...Shall I group both the PC3200 RAM sticks together and isolate the PC2700 one? Is that even right?
Please help guys, I really want to play all my games...

EDIT: I am not in the mood of buying a new stick of RAM...Also, my motherboard supports 4GB of RAM...So I doubt that this could have any thing to do with it...
EDIT2: Also, in my BIOS, the primary video adapter was set to PCI when my card is actually an AGP...so I changed that to AGP and then rebooted my computer...Could that be the reason? I am almost certain it is the RAM though...
Slot 1: 256MB PC3200 RAM
Slot 2: 256MB PC2700 RAM
Slot 3: 512MB PC3200 RAM
Slot 4: Nothing...
I am guessing there is something with that odd 2700 in there...As a result, whenever I run a game...say like NFSMW, I can access it for a while...and then I get a black screen...My machine stay's on...the only way to stop this is to manually reboot (press and hold Power button)...Funnily enough, this does NOT happen with FS9...I thought this was a PSU issue first, but it turns out it's not...
Also, this problem has never effected the system other than the time I play any games (except FS9)...
So, I was thinking...Shall I group both the PC3200 RAM sticks together and isolate the PC2700 one? Is that even right?
Please help guys, I really want to play all my games...



EDIT: I am not in the mood of buying a new stick of RAM...Also, my motherboard supports 4GB of RAM...So I doubt that this could have any thing to do with it...

EDIT2: Also, in my BIOS, the primary video adapter was set to PCI when my card is actually an AGP...so I changed that to AGP and then rebooted my computer...Could that be the reason? I am almost certain it is the RAM though...