Synching media to motorola i580

Question

I bought a motorola i580 from a co worker. There was music on it until I placed the SanDisc from the phone into my Lumix Digital Camera, which synched it and erased all memory. Now , my problem is synching music from MediaPlayer on my PC to the phone. It shows up as full according to the PC, but when I pull up the memory status while SanDisc is in the phone, it reads empty.