Hello Synok,
I am sorry to hear you are facing issue with the memory upgrade. Yes, indeed G.SKILL is a good brand. I would like you try installing just the 4GB modules; one module at a time (keep the rest of the slots empty) and repeat the process with the other module, only if you haven't tried it yet. Also update your BIOS to the latest version. I do not think that the above process will help you either, but hey why not give it a try?
Having said that, according to G.SKILL the memory which you are having is compatible only with motherboards having the following chipsets "Intel Z77, Intel Z68, & Intel P67" - (Click here!! - http:/www.gskill.com/products.php?index=346). There is no mention that it supports "Intel X48 Express Chipset/ ICH9R" which is the chipset of the original motherboard which comes with Vostro 430. You can try G.SKILL "F3-10600CL9S-4GBNT /F3-10600CL9D-8GBNT ", this might work with your motherboard (this memory is CL9 memory and not CL7). To confirm about the chipset you can check the dell specs from the following link - ftp://ftp.dell.com/Manuals/all-products/esuprt_desktop/esuprt_xps_desktop/xps-430_Setup%20Guide_en-us.pdf
If you have any question regarding the memory please let me know.
Good luck with the upgrade!!
Regards,
Xqzit.
