"I could not."
Translation:Ich konnte nicht.
http://german.about.com/library/weekly/aa032299.htm (see "Modals in the Past Tense")
The sentence could carry that meaning in English, but I wouldn't assume so unless I had significant context indicating that to be the case.
As a general rule, future constructs in English are much more explicit than in German. You almost always have to use the modal verb 'will' to express such meaning.
It is a general principle. There are other rules that also govern the position of verbs. In a nebensatz with conjunctions such as DASS or WEIL the conjugated verbs goes to the end with if there is an infinitive or participle it precedes the conjuagted verb. eg "Ich wusste nicht, dass John gut lesen kann."Things get even more complicated with multiple modal verbs in the past tense or with using passive.