Remember that verbs have several modes.
Function:
Running for president is a lot of work. (gerund)
To be or not to be, that is the question. (infinitive)

Using modals:
There are three forms of verbs:
1. Conjugated / for example: I eat, you eat, she eats etc…
2. Infinitive / for example: I like to see my friends on the weekend. (to see)
The gerund and infinitive forms are not set in time but they have the same meaning.
Remember sometimes you can use both forms (gerund and infinitive).

Structure:
use to + verb stem for the infinitive (to not + verb = negative)
use verb stem + ing for the gerund (not + gerund = negative)

Examples:
John asked if I wanted to eat with him.
Peter asked if I was having fun.