Iphone 4 not syncing music at all.

For the past few weeks, every time I sync my iPhone to my computer, my iTunes tells me that it cannot read my iPhone and that I need to do a system restore. I've looked around before and apparently there's no solution to this problem, so I restore my phone. Every single time I restore it I go through the process and set it up as a new iPhone and everything, but when it comes to syncing my music, iTunes won't do it. I've tried selecting and unselecting the songs, and manually managing it. Every time it goes through the sync steps and the 5 GB of music I have downloaded pops up on the bottom bar, but at the last step it goes back down to only having the "other" bar on my memory bar and it doesn't sync my phone. I'd really like if someone could help me with this, because it's becoming quite bothersome.