我一直说,不给上下文语境求翻译就是耍流氓,因为可能性太多了:
1. 如果没有特殊语境的话,I (或者其他人称代词) can't open the door. 就可以。
2. 如果有特殊语境让人可以推测出打不开的原因,则可以采用@夏曼迪老师的各种翻译,例如:
我开了锁,然后用力推了推,发现门打不开了。
I unlocked the door, pushed it hard and found it blocked.
我没有钥匙,门打不开了。
I don't have a key and the door is locked.
门打不开了,我们还是跳窗子走吧。
Something is jamming the door, we'd better get out through the window.
一阵风把门刮上了,门是自动锁的,现在打不开了。
A blast of wind closed the door. It is auto-locked and now unopenable.
3. 有语境的话还可以采用其他的意译说法,例如:
我辞职以后办公室的密码就换了,门打不开了。
After I resigned, the password of my office was changed and it is not accessible now.
让你出门遛狗不带钥匙,这下好了吧?门打不开了。
Why not brought the keys with you while running the dog? See? You've locked yourself out.
这地下仓库的门太重了,打不开了。
The gate of the underground store is so heavy and I am not strong enough to open it.