I just replace my secondary hard drive on my 1700 Mhz computer. I also added another 512 Mb of PC 2100 DDR SDRAM. I have spent the last 2 days trying to get things to work and now XP starts to load and hangs. After checking with the Microsoft Knowledge base, they seem to think that it is hardware related. Anyone know if there is a diagonostic software that runs in DOS mode. I downloaded a RAM tester from Microsoft. Naturally it does not run in DOS mode. I have already tried to repair XP and then totally reformatted and reinstalled the operating system. Please help.