If a car can move in reverse but not forward, it could be due to a few potential issues inside the automatic transmission. One possibility is that a clutch or band within the transmission has become worn or damaged, which would prevent the transmission from engaging properly in the forward gears. Another potential issue could be a problem with the torque converter, which could cause a loss of power to the forward gears. Additionally, it's possible that there could be a clog or blockage in one of the fluid passages inside the transmission, preventing the proper flow of fluid to the forward gears. A proper diagnosis would require an inspection of the transmission to determine the exact cause of the issue.