"my grandpa didn't work now."这个句子好像有点问题？

是的，didn't用在一般过去时当中，而now一般是在一般现在时中和现在进行时中，也就是说时态不对，和上面的老兄说的一样，可以改为my grandpa doesn't work now.
或者my grandpa isn't working now.

now是现在时 与do搭配
did是过去时 这样搭配当然不对啦

My grandpa doesn't work now.

呵呵明白了吧~~

my grandpa doesn't work now.
这样时态就对了

没什么问题