iPhone 4 refuses to play music. I press play, it shows the play icon next to the battery life icon, but immediately disappears. What can I do to fix this?

Hi duckylolz15!

Great work on doing a little bit of troubleshooting to start out with! I've got a couple of articles that I believe will help you with your issue. If you are having issues with specific songs that will not play on your iPhone, then you will want to refer to this article (the article is written for iPods, but will definitely work the same for your iPhone 4):

Troubleshooting songs that skip

http://support.apple.com/kb/ts3217

Specifically, you may want to follow the instructions listed below:

Make sure song files are not damaged

If a specific song skips when you play it, it may be damaged.

1. Delete the song and update your iPod.

2. Insert the CD you used to import the song and import it again. If the CD is scratched or dirty, iTunes may not be able to import the song. Try cleaning the CD or use a different one. If the song was imported or created using a third-party application, try the following:

1. Use iTunes to import the content directly from the CD.
2. Convert the content to an iPod-compatible format using iTunes.
3. Update your iPod with the new copy of the song.

Another step you may want to try can be found in this article, concerning issues with applications purchased from the App Store:

iOS: Troubleshooting applications purchased from the App Store

http://support.apple.com/kb/ts1702

The step you are looking for specifically will be this:

4. Restart the application

If the issue affects only a single app, try closing just that app:

1. Press the Home button to return to the Home screen.
2. Double-tap the Home button to display recent apps.
3. Tap and hold the affected app until the red minus appears.
4. Tap the red minus to quit the app.
5. Press the Home button, then restart the app.

If these steps do not help resolve your issue, you may want to visit getsupport.apple.com to get in touch with an Apple technician who will be able to help you resolve your issue. Thanks for using the Apple Support Communities!

-Braden

Try a reset: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps from the tray before doing the reset.

Also - you might consider deleting and resyncing (or re-downloading) the music tracks.

Have either you or braden85 noticed that the OP's Sleep/Wake button is broken?

I'm afraid your only option is to try restoring your phone, first from backup & if that doesn't fix things, then as new.

You can use iCloud to backup/restore your phone...make sure you have a fast WiFi connection. First, backup to iCloud, then, on your phone: Settings>General>Reset>Erase All Content & Settings...then restore from the iCloud backup you made when you started.