People are saying play boardgames and stuff, but I think your problem is more severe than that, and if want to enjoy this stuff again, you need to dial things back, and focus on being capable of what you need to be able to do to DM. Which is "make things up". If you can't make things up, if you're reliant, in the way you've described, on pre-gen adventures and following rules, you've basically lost what it takes to actually be a good DM.
I think RE here may be on to something. I will make a couple of alternate suggestions of things that might help...
1) Find a simple system that isn't mechanically too complex, and where you don't spend too long learning or engaging with the mechanics. You want to be kind of bored with the mechanics before you even start writing/running. If you're overly engaged with them, you're going to get the moment that ceases, and you'll lose all enthusiasm.
So, there's a class of games in which the process of play actually generates a significant amount of the content, and the process actually hands the GM the moment in which they have to make things up.
Cortex+ games are an example. If you are a fan of the Leverage TV show, there's an excellent and really simple game for it. When a character tries to do something, they pick up one die for an Attribute, one die for the Role, roll them, and add them together. If one of the dice comes up a 1, that's a time the GM may choose to make up a complication.
The adventure itself is just an outline, and dealing with the complications actually fills in most of the details.
Or, you can take one step back from that. Once Upon a Time, from Atlas Games, is a card game in which you build a story out of prompts on the cards. Don't worry about rules and characters - get back into practice of generating cool stories from elements at hand.
2) Write your own campaign.
Or, alternatively, don't. Run a game that does not call for a "campaign". Like, say... Toon! Or Paranoia. Or an episodic superhero or Star Trek game. You may find it constructive to revive and explore the fun of individual sessions, and not worry about generating or maintaining a campaign as a whole.