Doubled Up Music iPhone 4 iOS 7.1.2

Hi.

I recently rebuilt my desktop, and I added all my music from my backup on my portable hard drive, to my new one.

Added it all to iTunes just fine, iTunes detects my phone and everything.

Now here's the problem.

On my desktop, I cannot delete music or add music to/from my phone.
I can see it in the device's music list, but nothing can be changed.

I also have doubles of EVERYTHING. I tried swiping to delete a few of the doubles, but it gets rid of the song itself.

Now before I had rebuilt my desktop, I was using my laptop for adding music/etc to my device.

Both computers I have are authorized with the itunes store, yadda yadda yadda.

It's all under my own account.

Since my desktop is my primary system, I'd rather use it to sync my music to my device, instead of having to piddle around with my

sub-par laptop.

Any suggestions on how to remedy this?

I have the "sync all music" unticked in itunes under the device.
Can't even delete any of the music to re-add it either.

Thanks