I am finished with the seventh badge, and already beat team galactic, after that I dont know where i'll go?

Ha? Get gym badge electric. After get eight badge you can beat EV! After credit roll, go shark mountain to finished story line. And get all avaible legendaries pokemon. You beat ice gym leader? After there go top mt.coronet and follow storyline. Beat ev if you can.

After beat ev you can unlock many event. In victory road blocking road, cresselia, get uxie,mesprit, azelf, get dialga and palkia, mining, caught all pokemon, colecting berry, get bp, beat rival, get heatran, more. Explor all location, you can find secret. Colect plate, and if you have gba games is have more event.

If you defeated team galactic at the lakes, go to Veilstone to defeat their lab. If you have already defeated them their you need to go to Mt. Coronet through Route 207 and use surf to continue to the top of the mountain, defeat Team Galactic, and enter the Distortion World. Go through the Distortion World, defeat Cyrus for the last time, and battle Giratina to capture it. Make sure you remember that it is a Ghost Dragon type and this is your only chance to capture it. Having done that, you can either attempt to catch all the pokemon of the lake (it doesn't matter when in the game you do this now), or go to Sunyshore City to obtain your eighth gym badge. To get to Sunyshore, go to Valor Lakefront and head east to a newly opened area.

If by defeated Team Galactic you mean:
- Defeated Cyrus at the base in Veilstone: go to the top floor of Mt. Coronet (lower), which is Spear Pillar, then go through Distortion World, where you confront Giratina (you can confront again after defeating the Elite Four, it keeps respawning every time you do so). Defeat or capture Giratina to continue.
- Finished going through Distortion World: Go to Valor Lakefront (Hotel Grand Lake), east of Pastoria, and head east to Sunyshore City, earning your eighth gym badge. From there, Surf north to Victory Road and the Pokemon League to find the Elite Four.
Keep in mind that you can now also capture Uxie, Mesprit, and Azelf by visiting them in their caves in Lake Acuity, Lake Verity, and Lake Valor, respectively.