
At first clean all contacts, i.e. all metal parts that touch the batteries, buttons and case. Gently scratching them with a small screwdriver until they look clean again should remove all invisible oxidation on the metal parts. Also check with new brand batteries, especially some cheap ones that are "who knows how old" as sold cheap might already be dead when they come out of the package.
If there are still no signs of life then give the watch a few hours with the batteries in it. Sometimes it takes some time until a watch starts running again, especially if it was left for decades in a drawer or so.