We've all been blessed with the ability to hum, whistle, grunt, moan.......Guitar is a completly different person isn't it.....or is it. I'm sure you find yourself humming a tune at the least opportune moment. A time when you don't have a guitar around to put a chord to it. I carry one of those small microcassette recorders around with me and hum or whistle or all of the others into it until I have an opportunity to get it on paper. (bad memory here)

Also remember that inspiration doesn't just show up when we call it. For me at any rate it comes in waves. I'll write for a day and not have anything for a week. Or write for a week and not have anything for a month. The more you push inspiration the more it comes. Until.......it's gone. Then we sit around and wait for it to recharge it's batteries.

As for a start. I'd record my most basic changes. (I,IV,V) for example onto whatever you have. Even throught the mic on a portable. Listen for sounds outside the box and try to build a melody on your chords. (with or without and instrument) Find the notes within the chords rather than the root. Find the interplay and play with those.

Good Luck, All the best!