Let me ask you a couple of questions.

After replacing the batteries, did you set the camera back to the M90
or B on the shutter speed dial?

Did you check and make sure the connections were clean?

Are you sure the batteries were fresh?

Some of those should be apparent but sometimes folks over look them.
Having fresh batteries and cleaning the contacts, both top and bottom
in the battery chamber, are some of the most frequent goofs.
The resetting of the shutter speed dial tp M90 or B was Nikons way of
clearing any charges left by the old power supply and readying the
electronics for fresh power. (At least that is how it was explained to
me) Not many FG users know that little trick. But, if you have done
all that, then a trip to the repair shop might be in order.

Good luck and I hope this helped.

Draco