Where should I go with this now? Feeling lost!

I have literally never been so stuck on a plot in my life ...

I decided to go in a different direction to what I'm used to for my latest project and base my novel around three young witches (either just finishing school or just starting university, haven't quite decided yet) living in the present-day English suburbs, where no one knows magic exists. I know loosely what I want in terms of character development, but what I need now is some sort of external conflict to drive them all.

What I'm thinking of right now is that one of the witches (say, Witch A) has a bit of an infatuation with her friend, Witch B, and tries to brew up some sort of love potion or cast a love enchantment. However, Witch A gets it all wrong, or perhaps follows the instructions of a dark grimoire mistakenly, and she angers the forces of magic, the spirits of previous witches which live on in nature. I guess then I want something these forces to take action against these three witches and threaten their town in some way. Maybe with a witch of questionable intention (AKA villain) manipulating these spirits and encouraging them behind the scenes.

But that's as far as I can get! I don't know what the spirits could be doing that is such a pressing threat, and thus I have no knowledge of what kind of journey the three need to go on to rectify the problem...

Ideas, anyone?? I need a push in the right direction, I'm stuck in a rut!

What sort of powers do these spirits have? For example, since they are in nature, can they cause earthquakes and stuff like that?

Yeah, it could have some kind of, "Don't mess with nature, it'll COME BACK AT YA!" morale. Like destroying technology is something they could do.

The magic spirits will only allow one of the three into college (university?).

Witch A's story goal: to gain admission using human powers only, she is challenged by temptation to use magic.
Witch B's story goal: to gain admission using nothing but magic, she is challenged by incredulous achievements.
Witch C's story goal: to sabotage the other two candidates, she is driven by rebellion and a darker force.

So, the three of these character appear before an admissions board where one of the scholars is a witch but the candidates do not know which one?

I can see plenty of conflict with those goals, I just don't know if the university details fit into your story world.

the tried and true waking up an ancient evil, which the witch spirits worshipped in their day.