I got ahold of a Dell XPS200 Desktop and am trying to update the ram it now has 2 cards of PC2-4200 and 2 of PC2-5300 all are 512 MB. I got given 4 1GB cards that are pc2-4200u DDR and assumed they would work as it already accepts the 2 PC2-4200. But when I install any of the 1GB PC2-4200 the computer alarm sounds and it won't boot. Here is a screenshot from crucial showing what this computer accepts. I just wonder why it won't accept the PC2-4200 1GB when it accepts the 512MB 4200. Can I update bios or try something else. I sure would like to have the fre 4GB ram if possible.