F450 flipped during takeoff

Hi all, I am currently using F450 with pixhawk2.4.8. I tried flying in STABILIZE mode upon all the calibration but my drone either couldn’t take off, or it will flip over when i’m pushing the throttle stick up. This issue has been for almost a week and I can’t find the problem. I have checked directions etc. It could not be an overweight/under power issue as the drone carry the usual stuff like pixhawk and battery - and the battery is fully charged.

Motor: JMT F15843
Prop: 9443
Battery is 2200mAh 3S1P 30C
Takeoff weight: currently at 1.4kg


Please help me and I thank you in advance.
Backstory: Previously using APM2.8 and i managed to fly normally.