power problem,dell dimension 4400

Nothing Happens when I push the power button. There is a green lite on the motherboard. What does that mean? Had recent lightening strikes here in Northern Cal.How do I test the PSU? No diag lites lit on rear. No hard drive light on. no power button light on. Will the lights on the Hard drive and the power button light work if the motherboard is fried? How do I test the motherboard?
Thanks!!!

In a case like that, I automatically change the power supply. I only had it tested once. I paid someone $10.