Be sure it’s not overheating, verify all fans are operational and pushing air in the same direction. Consider reapplying thermal paste to the heatsink (remove old paste, clean with rubbing alcohol, power blow surfaces, apply thin layer of new). You can flash the firmware by microSD card to the latest version G2.54. Swapping a failing PSU with a functional PSU, preferably 20A or better (this solution being best). And finally, if none of the aforementioned works, you can change the control board.
From this heavily troubleshooted thread with all of the possible solutions we know of: iPollo G1 Mini – Not connecting, no LED lights after reboot