If you press power button absolutely nothing happens? No fans start, no lights blink?
Assuming nothing happens, try these:
1) unplug RAM from motherboard
- If there's a sign of life RAM is dead
2) unplug everything non-essential from motherboard (HDD drives, DVD drive, graphics card and all other expansion cards)
- If there is a sign of life, something you pulled out is dead, try plugging the parts back in until you find what's broken
3) unplug everything from power supply except DVD drive and try
starting it with a paperclip
- If there's a sign of life either CPU or motherboard is dead
- If there's no sign of life, at least PSU is dead