In pre-hard mode I found all the Crimson hearts and destroyed them, and now in hard mode I can't find any shadow orbs because I never found any, so now I can't get any new orbs or ores and the dryad keeps saying that my world is 7% Corruption. Can someone help me?
Destroy Crimson/Demon Altars to get Hardmode ores, not Shadow Orbs
Shadow Orbs are the Corruption equivalent of Crimson Hearts, serving the same purpose (but dropping different items), and neither has a purpose specific to Hardmode. After defeating the Wall of Flesh, you'll receive a new hammer called the Pwnhammer, which can be used to destroy Demon or Crimson Altars in a Hardmode world. Destroying Altars is what causes new ores to spawn in your world, not Shadow Orbs or Crimson Hearts.
As Altars are the crafting station for various items (mostly boss-summoning items), you should keep one that's relatively easy to reach intact so you can continue to use it as needed.
Shadow orbs are the corruption counterpart to Crimson hearts. If you want to get hardmode ores, use the Pwnhammer from the Wall of Flesh to smash Crimson alters. However, crimson alters are crafting stations for some things, so you should probably keep one that you can easily access. Also, if you smashed Crimson hearts, you should have Crimson, not corruption, so your Dryad should say your world is 7% crimson.