Different usage of the simple past and the past progressive
The past progressive on its own refers to an action in the past whose course lasted an indefinite amount of time. The implication being that noting noteworthy happened.
for example: Yesterday I was watching TV. ( nothing special was on)
the simple past
The simple past refers to an action that took place at a certain point in time in the past.
for example: Yesterday I saw a great John Wayne movie on TV. It was awesome.
simple past - past progressive - difference
The past progressive is mostly used in connection with the simple past In this context, two actions take place at the same time in the past, one of which takes longer, the other is shorter. The shorter one interupts the longer one.
for example: When I was watching TV, somebody rang at the door.