From the manual:

2 beeps:

• No memory modules are detected.
• If two or more memory modules are installed, remove the modules, then reinstall one module and restart the computer. If the computer starts normally, continue to install additional memory modules(one at a time) until you have identified a faulty module or reinstalled all modules without error.

And use canned air to clean out all the dust bunnies.

Green +1, 2, 3:

• Another failure has occurred.
• Ensure that all hard drive and optical drive cables are properly connected to the system board (see the "System Board Components" section for your computer).
• If there is an error message on the screen identifying a problem with a device (such as the floppy drive or hard drive), check the device to make sure it is functioning properly.
• If the operating system is attempting to boot from a device (such as the floppy drive or optical drive), check system setup to ensure the boot sequence is correct for the devices installed on your computer.

When was last time you replaced motherboard battery?

Amber LED on motherboard means the board is getting power from the PSU...

More precisely it means that FLEA  5VSB power 20W is available.  It does NOT mean that the power supply is OK.

Most common 123 problem is invalid video configuration.