My system specs since I know it will help. Asus CG essentio 5270 bestbuy refurb. Stock parts .75 tb HD unsure of brand Nvidia gts 220 gpu intel 2.5 ghz core 2 quad processor 8 gb ddr2 ram, crucial mem scan shows the followingDR2 PC2-6400, DDR2 PC2-8500, DDR2 (non-ECC) Dvd-Rw drive OS Win Vista premium, 64bit Non stock parts 2tb wd caviar green hd Lately I have been having an issue where I leave my pc on, my energy saver function turns my screen off, and while the screen is off, randomly it will crash, doesn't do it all the time, amount of time doesn't seem to matter as I have left it like that over night and it was fine, but earlier tonight I left the room for about 20 mins and when I came back it was unresponsive. Every time it does I have to hard reboot. I have tried to run memtest86 from USB and it wont load, not sure how to get it to burn to DVD as I have tried and nero says it's the wrong medium for this file. Fairly certain my ram is going bad since it is a refurb. What I need to find out is if I can put DDR3 in ( when I first bought it It said DDr2/DDr3 ram) so I am unsure if It will handle DDR3, oddly the ddr3 is cheaper by about $200 I also am wondering, do I have to buy a 4 card set or can I get two, two card sets as long as they are identical?