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.

Does it come up with the boot splash screen? Can you access the BIOS? If not, it's time to send it in for repair.

Problem might be a power supply error or a faulty motherboard. Check the Cd drive and the CPU fan to see whether these parts cause the problem. It can be any bad components, you can test it out by switching parts and replacing it with a spare one from another laptop to see whether the part works all the way.

Hi again - fans working. I tried another monitor to rule that out, the other monitor didn't work. Could it possibly be a blown in-built graphics card? I am thinking of getting a new PCI graphics card.

You said the onboard diagnostic lights indicate a problem with memory. If that is the case, then changing the video hardware will not likely help. If you don't get a boot screen so you can go into the BIOS setup, then you need to send the system in for repair. Contact Dell for tech support. Their online chat with technicians will usually determine what you need to do, and whether or not you still qualify for warranty repairs.