I wanted to add more RAM in my PC. Presently it has (2) Kingston KVR800D2K2/2GR PC6400 in slots B2 and A2, and (1) Kingston KVR800D2N5/1G which were working fine. I wanted to replace the old memory cards with (2) 2 Gig memory cards which will give me 4 Gigs. Frys Electronics did not have the Kingston brand so in order not to mix brands I decided to get a Patriot PSD24G800KH (2x2 Gb) Kit. It did not work. I tried it three times. I put the old cards back in and the PC worked but when I replaced the Kingston cards with the Patriot, it did not work. The monitor would not even come on. It's possible that the Patriot cards were defective but that's highly improbable. I checked my connections and follow instructions from the User Manual but no joy. I have fifteen days to return the Patriot cards but before I do that I'd like you guys' opinion.