Tying your heli down isn't the best idea.(I personal feel like it dangerous)
I know it's fixed pitch but don't know much about it.
It sounds like something changed like a setting in the radio or linkage something is broken.
Did something happen from the time it was flying to now?
My Falcon 40 flew well for a short time. Now with a fully charged battery, it will not get above ground effect no matter how far I advance the throttle. The blades seem to be spinning fast enough to generate lift but no go. If anyone can tie their helio down and measure the rotor rpm at full throttle, it would be helpful.