Hi and welcome to Geeks to Go. Does the power supply fan run when you power it up? This would be the place to start. Any cable connection (a conductor) at the computer is a possible conduction path for voltage/current during that lightning strike. Fuses and surge protectors do provide some protection. You mentioned the modem was burned. This has a connection to the phone line. The lightning voltage entered your computer through this path (maybe others as well). Hard to tell how much damage. You will need to work your way through this component by component. A multimeter (DMM) would be helpful. If you turn on the power supply and its fan runs, and there is voltage present on the output cables that connect to the mothboard and other components, it is ok. Then move on, step by step, component by component. Next would be examining the motherboard, once you are sure there is power to it.