Power Supply failure, the darn thing just wont turn on. Usually preceded by a popping sound right after attempting to turn on. In addition to the pop there is usually a hot smell and possibly faint smoke. Check out this Link1 Link2 if you want to take a crack at repairing. I find this to be a waste of time since in my experience (8 out of 8 tries) the fuse blows for a reason and if you do not fix the cause it will just blow again.
If you are getting the spark and crackle when you plug your power cord in you want to xbox power supply repair tutorial.
Or swap it out. Available Parts
If you do not mind a ugly pile sitting next to the TV you could try to use a standard AT power supply.
Here is a pic of a Delta Power Supply on top and Mineba on the bottom
10/19/03 recent questions about lighting and whether a power supply will resolve the problem
All power supplies we carry are distinguished by console version and are otherwise interchangeable. The manufacturer makes no difference, to keep costs down we do not distinguish between one brand and another when stocking/shipping. If you order a power supply and install it I suspect you will have a working Xbox again. Occasionally not, sometimes the lightning may have damaged the mother board as well. I always feel guilty when telling people what to do I would guess 75-90% of the time the power supply fixes it but if I answer 100 mails that's like 10-25 people that followed what I said and it didn't work out. Did everything in the house get fried, only the Xbox or the Xbox and some other stuff? I think the degree of damage to other appliances may give you some clues, if the lightning struck the wire between your house and the pole I would say that is the worst case and everything in the house probably got ruined including the motherboard, if the Xbox was the only equipment affected I would say that is the best case and replacing the power supply will probably fix it.