Instead of ideas (which I can also give you some if you really need them), here's some advice to come up with an idea:
- Find a game you want to play, and then make it your own.
- Another way would be to decide on the type of game you want to make (platform, puzzle, point and click, fps, etc.) and work on the finer details later.
- If you had any larger-scale game ideas, you could always boil it down to its most basic identity and work with that.
- Lastly, you could always partner up with someone who already has an idea, resolving your problem completely.