I know how hard it is sometimes to just get started on something. There always seems to be a ebb and a flow when it comes to making music. Either you cant stop, or you can't figure out where to start. I have been on both sides of that fence. When you can't stop, that's not too bad. It's when you can't start, that's when you want to start pulling your hair out and punching walls. Over the past few years I have figured out ways of starting up the creative process again. They don't always work, but sometimes it's enough to get you over that hump and start making music again. I hope these help.
1 - Listen to other people who make your same style of music
Sometimes it helps me to listen to other peoples stuff. It gives me a chance to relax and let my mind wind down. Once you clear your head, you can start to listen to the different sounds, chord progressions, drum patterns and other aspects of the music. Even if you just pick out one thing that you like and try to mimick it, that might help you get started on making sweet sweet music again.
2 - Get out, but bring a note pad or recorder
Sometimes I think of some of the best melodies when I'm in my car on the way to work. Again, when you let your mind go, that seems to be when ideas start to hit you. Go hang out with your friends, go see a movie, go to the beach or just go for a walk. But don't forget to bring something to write or record the idea when you get it, you may never get it back again.
3 - Network with other musicians
Part of what makes me progress as an artist is meeting and talking to other musicians. Everyone has their own take on everything, and if you sit down and chop it up with someone who is in the same genre of music as you, you might pick up something you never thought of before. Sometimes that little spark is all it takes to make the creative fire start burning. If you don't know where to meet musicians around where you are then try going to forums and groups online. That has been helpful for me in the past.
4 - Show people your stuff
Sometimes it helps when you let people hear your music, even if it isn't finished. Ocassionally the feedback is enough to get you motivated to either change the song you showed them, or start on something new. Anytime I show people my new stuff and they like it, it puts me in a productive mood. At that point I take it and run with it.
5 - Go back and listen to old tracks
From time to time I like to go back and listen to my old music. This shows me how much I've changed and grown as an artist over the past years. Good or bad music alike, it could help you break out of the rut and get back at it again. Just hearing how you have progressed might get you going enough to move on to the next phase.
Hope those tips help! Keep checking back for more!