Dell Optiplex GX280: Solid amber light?

I picked up a Dell Optiplex GX280 from a local thrift store, hoping to use it as a secondary computer to run Ubuntu on. Obviously, I expected some problems. When I turn it on, the power light goes solid amber, and the CPU fan starts getting louder, to the point where it sounds like a jet engine, and it doesn't POST. I tried everything I could think of. I unplugged all peripherals, and tried different RAM. Still solid amber light. CPU fan in jet engine mode. No POST beeps at all. Google was no help. The hard drive has a slight clicking sound, so I know it's failing. But I still get the same symptoms even with it unplugged. What could the problem be?