Simple version (Apple official version)
1) Shutdown your 5,1.
2) disconnect the power plug
3) wait 15s, connect it again
Done!
Expanded version (more steps than Apple's version, but no harm anyway).
1) Shutdown
2) disconnect the power cable
3) press and hold the power button for 15s
4) re-connect the able
5) wait another 15s
Done!