Hmmm... I'd say:
1. Keep trying to write at least a little while every day, because sometimes you just have to sit in the chair and work at it to give an idea the opportunity to appear.
2. But be sure you aren't doing nothing but work. If nothing is appearing in your brain, it may need some new outside stimulation to get the ideas started again, so take time to go for a walk, read new books, go out with friends. Put yourself in situations that are rich for your physical senses in new ways so your brain will start creating new pathways, even if that just means trying a different sandwich for lunch. You don't have to take a two week vacation, but find at least a little novelty every day.
3. Make sure you have the right physical environment to work in. I need to be somewhere comfortable, quiet, and alone, so I can hum out my ideas. I have to be able to hear it out loud as I'm working to get the next part of the idea to come. Maybe you like the background hum of the dishwasher so it isn't too quiet in your house, or to know someone is in the next room so you don't feel too lonely.
4. If all else fails, try listening to some music you like and singing along on a harmony part. Then shut the music off and keep singing your harmony. It often develops a life of its own and becomes the start of an idea.
5. Sometimes you can't think of a beginning, but you CAN think of a middle or an end, so go ahead and start with that part and then work backwards.
6. Some of the best works by famous composers are based off of simple scales, and key changes. Don't be afraid to write according to basic principles as a start. What you add to the texture can make that incredibly exciting. Writing absolutely according to expectation with respect to chord progression, and then denying the listener the resolution is a wonderful tension-creating device that keeps a work moving and developing when you are stuck.