Songs grey and white won't play or delete on iPhone 4S?

After I updates and synced, some songs turned grey and other remained white. All the grey ones won't play or delete, and about half the white songs won't play or delete either. I tired resyncing the songs back on the iPhone so I could delete them, but I only ended up with duplicates of songs and I could only delete the one I had just added? What is wrong? How do I fix this? 10 stars guarunteed to the person that can successfully help me solve this!

My iPod does this too but what I do is hold down the home button and lock button at the same time for a around 15 seconds. It resets it but doesn't delete anything I promise.