HDD LED and fan led started to flash after turning on the UPS

[Chapapa07]

That has never happened before, I was able to turn my pc on but thats something I couldnt ignore.

What could it be?

 

[95Viper]

Here is a couple of things you may want to check on.
You may need a meter to do some of this; and, know how to use it properly!

What UPS?
Is the battery good in the UPS?
Is it true or clipped sine wave?
Any other suppressors or filters on the line anywhere?
Good grounding or any/no grounding?
How many devices(what devices) are connected to the UPS?
What is your power source (generator, electric grid, etc.) ?
Is it using auto-sensing for voltage or do you need to set it manually?
If you take the UPS out of the equation... does it still have these problems, now?
How is the voltage & current at the point where you are connecting the UPS?
Did you try re-setting the motherboard and check your voltages at the PSU with the UPS plugged in and with the PC plugged straight to the source(socket/wall plug)?