I have an Studio XPS desktop that won't boot into Windows, startup repair doesn't work, System Restore fails. I have run Dell diagnostics on the system and it's really strange. When i do the Pre-boot System Assessment the Hard Drive DST says Warning - Hard Drive - No Hard Drive Detected.

Intel® Core™2 Duo Processor E6600 (4M Cache, 2.40 GHz, 1066 MHz FSB) Intel® Core™2 Duo Processor E6700 (4M Cache, 2.66 GHz, 1066 MHz FSB)

I currently have 2 GB RAM (1 GB X 2). I tried to install 4 GB more (2 GB X 2) and my computer would not initialize after power on. Is it even possible to upgrade this computer? Do the larger sticks have to be installed in the first to slots? I have never worked on a Dell and this has me stumped!