PC will not go to POST

After installing an exterior 3COM modem & during dialup to my my work network, suddenly my my OS (W2K) hungup, after attemping reboot my PC powers on but will not even register a POST screen, my Hardrive lights up but no detect of anykind. I’m thinking my motherboard got spiked thru the phone line somehow. Any ideas on how to test motherboard before replacing. Thanks