1. SMC reset
Problems solved: Fans blowing with no activity, machine is not booting, power button pressed and nothing happens, problems with indicators, Magsafe has wrong lights, battery is not charging, monitor and graphics issues etc. If the battery is not charged (from like letting it sleep too long), let the Mac charge up awhile afterwards.
Will not hurt the machine resetting if it's not broken.
Other related hardware problems (optional):
Check battery status: Hold option/alt key down while clicking on the battery icon in the menu bar, top right corner.
Magsafe: Use the correct/matching power supply charger with your Mac, not a less powered one from another Mac.
Further diagnosis from this select group of rescuers can be attained by opening Apple Menu / About This Mac / More Info / System Report / Power and snipping & pasting the Battery Info section (or the entire pane, for good measure). That will yield more insight as to how your Mac's battery is faring.