can or could

Technically I think it's 'could' because the conversation was in the past, but these days either sounds quite natural.

Can. It sounds natural. Could sounds weird. But then again I have never been a big fan of using could, it sound weird. Just like good, I never use good.

My close friend told me that I would not be able to solve the problems on my own and only God could/can enable me to solve them.

Which word in bold should I use? Is the sentence natural?

+++++++++++++++++++++++++++++

Yes, it's a natural sentence, Ms Tan. Either can or could can/could be used. 'can' illustrates that the speaker is being more resolute, more sure while 'could' shows a more tentative approach.

Many thanks to all of you.

Technically has nothing to do with it, MonaL. The conversation was in the past and this is a report [reported speech] of that conversation, using the reporting verb 'told' but the underlined portion holds either a specific future reference or an "anytime this situation arises" reference.

Both would and could hold future meaning. They can do this because in modern English, the modal verbs are tenseless. Hundreds of years ago, the modal verbs did have tense but that no longer the case.

Any of the modal verbs can operate in any time situation and could is not the past tense of can, nor is would the past tense of will, nor should of shall, nor might of may.

They are all tenseless.

Sorry, I should have written the "italicized portion", not the "underlined portion" in the post above this one.