iPhone 4 is stuck in a boot loop, has a broken power button -- how do I put it in DFU mode?
If your iPhone is stuck in recovery mode, DO THIS: (ON Screen USB pointing to a CD with a Music Note).


Make sure your iTunes is up to data, if not re-download itunes.
after re-installing ITUNES, plug your iphone via USB into your computer. ITUNES will automatically pick it up and a pop up box will probally say that your IPHONE is in recovery mode would you like to restore?
Click the restore tab.
Note - If ITUNES if out of date, this will not work.
Note - Do not do this over WIFI
Note - Do not interrupt the restore
Note - If you did not make a previous back up, your IPHONE will restore back to the factroy settings.  


All this happened to me, fortunately I made a back up. I hope this helps.