For large parts of Star Wars Episode V: The Empire Strikes Back, the Millennium Falcon is in pretty poor condition. Han and Chewie are desperately trying to fix it on Hoth while the Empire is attacking the Rebel base, and throughout the rest of the film it struggles to go into Hyper Drive.
But what caused it to be this way? The ship seemed to be in fine condition at the end of Star Wars Episode IV: A New Hope.