My pumpkin plant get flowers but then go brown and

fall off. is that normal? If not, why?

they will that is the male they die after the bee fertilizer the female the flower with the bulb at the bottom

If male flowers then yes. Female, no.
Female flowers have a lump behind them, males a long skinny stalk.

If in pots:
The roots may be damaged or killed by heat from any or all of these: direct sunlight on the pots; high ambient temperatures; and reflected light and heat from the surrounding surfaces.

Root space is restricted in containers, thus putting large plants at a disadvantage; less than adequate root room translates into insufficient absorbed moisture for the top growth.

Ensure soil is fully moist at the beginning of each day .

Actually it is highly likely they are not being pollinated and you will need to hand pollinate them. Plenty of how to threads on here.