[Mattheyu]

I'm flashed back to stock for repairs, so I guess it could depend on your rom, but there should be an option under Settings -> Connections -> USB to PC. If "Enable advanced network funtionality" is enabled, disable it and try again. And of course, make sure the "ActiveSync" radio button is selected, NOT Disk Drive.

I assume you meant "Windows Mobile Device Center", not ActiveSync. I remember tons of issues with that when it first hit, but I'm not familiar with it nor it's current state beyond syncing a couple of times. There have been instances where I just had to completely remove ActiveSync off of my WinXP install and reinstall it to get it to sync with my old Titan. If all else fails, try that?