If it's not beeping or running the POST I would start by suspecting the processor.
Make sure it's seated properly, take it out and put it back in, kick it, stuff like that.
When you take the lid off do check that the fan on the processor is running. If it isn't then there's every chance that the processor has been cooked.
Getting more technical - if that doesn't get it going or if the processor fan has failed, you might try swapping the processor that you know works - if you know where there is one.