1.拿不了=拿不動，意味超越你的能力，所以移動不了。 2.拿不下去，礙於某種原因讓你無法移動它，或許你是有能力移動它，但途中有某種障礙阻擾你。

The question you asked has a kind of means in China in different cases ,for example ,“东西”.In Chinese ,It can be interpreted as direction in some cases , can be understand as a thing sometime and also can be uesd to bite your thumb at somebody when you are very angry .The upstairs explain is good .

拿不了 = ability 拿不下去 = direction

1.拿不了？= too heavy to carry. 2.拿不下去？= depends on the conversation. can be "some attachment can't be removed", better to know the back and forth before give you a good translation.

拿不了： means that they r too heavy or too many that u can't take it . 拿不下去： means u can't take it downstairs.