Wake up a PC on your network with your iPhone using Mocha WOL
First make sure your computer is setup to wake on lan in your BIOS setting. To check this, press the 'del' key (or F2, F10) when your computer starts to enter the BIOS. Verifiy that Wake on lan is 'on' then save and restart.
Now install Mocha WOL by MochaSoft from the App store on your iOS device and add the PC's IP address and MAC address to the app so that next time your PC is off you can turn it on with a press of a button on your iphone