Wont boot after running out of power

Usually that loading bar means running disk check or trying to recover from a power save deep sleep. Charge battery for a while then do smc reset and pram reset then Try holding option key at boot and try going to recovery partition run disk check and repair disk permissions see if that work if still doesn't work try using installation disk again sometimes when booting to CDs it takes a ridiculous amount of time seen it take as long as half hour just to boot to a dang cd so be patient and wait up to 45 min to be safe if still doesn't work. If have another Mac you can try to boot with the other macs hd in yours and vise versa. To verify if can boot to either drive. Then if not try to get your hands on an apple hardware test cd for your model of laptop test hd and ram