Utility LED flashing green/red

Seems like your Battery is very low. Try charging the battery for a few hours. If the problem persists, it maybe the time to get a new battery.
Like all batteries, UPS Batteries (that store electricity and let s you use it in case of a power failure) have a limited life. This life is averaged to be around 2 years. So in case your UPS has been in use for approximately that much amount of time, the battery is in a near death situation.

For instructions regarding replacing the battery, please refer to your UPS Manual.

PS: Also, I have noticed this kind of behavior when the UPS is connected to a socket powered by an Inverter. This kind of behavior is observed when the Inverter battery is running low.