First, check if the media is not defective. Look for scratches or cuts on the disc surface. If the disc is OK then try to play another disc or game. If the problem still occurs then perhaps it is time for you to have your gear examined by a qualified technician or returned to the store (if its still warrantied).
Freezing or hanging can be quite normal in some games in PS2 but if all of your games freezes every time then there could be some issue with the hardware. You can try using some clean & new games & if then also you get the same issue you can take your PS2 to the service center.
First, make sure it isn't the disc that is scratched or dirty; if it is, then clean it. You can try using one of those air dust blowers and spray it into the disc part of the PS2. If that doesn't work, try turning the PS2 sideways.