Hi, I have dell dimension 2400 that won't boot. Diagnostic lights are y,y,g,g saying trouble with memory but no beep error. I opened case and cleaned, reseated all. Unit gets power with front power light green, fans spin but nothing to monitor and keyboard lights aren't on, disconnected dvd drive, same. Looking at the microprocesser under the heat shrink, it's chalky on top.... is that normal? Was thinking of replacing power supply but have no idea how to test it. Please help.