Here are the three best things I always do when my mind decides to stop working and I need a few ideas for a new story to start writing...
If you're stuck, listen to a song, decide what it's about, and write about it. For a more complex story, listen to three different songs. One song is the beginning of the story, the second is the subplot and the third is the ending.
For me, I usually Google the lyrics after I've decided what I thought it was about, to see if I get any more ideas from the lyrics. Because sometimes I make lyrics up. And with other songs, mumbling for thirty seconds just isn't as inspiring as reading a paragraph of good lyrics. Music can be the most inspiring thing.
I got this idea from my writing class. Make two lists, one of settings/locations and one of feelings/emotions. Cut each location and each emotion and make two piles with them separated, then pick one from each pile. From there, make a title. For instance, The Dungeon of Love or The Bedroom of Fear. From there, free write as much as you can. It's surprising how inspiring it can be to have the theme of the story already set out for you.
If you want, you can change the lists. Instead of locations, have characters. Or add it as a new list. You can add tonnes of things to complicate your basis, like date (eg. Ancient Roman, Future, Present, WW2 etc) or reader's age (eg children's story, OAPs, middle class adults, poor teenagers etc) or random objects that need to be important to the story (a cow, an iron, a television, a dog, etc)
Interesting note, someone from that class got "The Toilet of Happiness." ... However, he chickened out and changed it. Boo!
One of the best things to do if you're stuck is to draw upon your own life. Have you been told a funny story recently that you could adapt to be a short story/novel/poem? Have you been through something unique or unusual recently that you can turn into an entertaining (or even therapeutic for yourself) story? For example, a bereavement, an illness, a new job, a new hobby, moving city, a holiday etc.
Even if you're someone who thinks they have a boring life I guarentee if you think hard enough, you can find something in your memory worth making into a story.
I hope I've helped! If you're still feeling stuck or need any kind of advice, email me at email@example.com and I'll get back to you as soon as I can.