i have a new windows computer, when i sync my iphone 4 all my music wont transfer, just my purchases

iDevices are not backup devices.

Copy the ENTIRE iTunes folder from the old computer to the new computer.

The iTunes folder in question are located here:

Your iTunes library files track the media you add to iTunes, how you've organized it, and other information such as playlists. By default, these two files are in your iTunes folder:

• Mac OS X: /Users/username/Music/iTunes/
• Windows XP: C:\Documents and Settings\username\My Documents\My Music\iTunes\
• Windows Vista: C:\Users\username\Music\iTunes\
• Windows 7: C:\Users\username\My Music\iTunes\
• Windows 8: C:\Users\username\My Music\iTunes\

Moving the iTunes folder that contains the actual program would do absolutely nothing and certainly would not allow the program to run.

Install iTunes on the new computer before or after moving the ENTIRE iTune folder referenced above.