Wepons and gear change from earned to stolen
I got Skyrim and after a while 90% of my gear that I earned by beating quests now say that are stolen. so I have no idea how to fix it. Any ideas ?
The above comment about the item being stolen because you dropped it somewhere that a person can claim it (i.e. their home) to inventory-manage is true. NPCs in Skyrim will warn you they've flagged the item as theirs if in range. They'll say something along the lines of "well, if you're not going to use it..." and take it or claim it. This happens less often than them accusing you of littering, but once you start pulling unique items, it happens more and more. NPCs tend to keep high valued items if you throw them away. My guess is that you have tried to just carry every awesome weapon you've earned and ended up playing Inventory Management Simulator while standing on private property.
No matter how you got there, the fix is simple. And expensive. Oh, and neither is it simple if you haven't done the Thieves' Guild quest line, as you need the fences (merchants who buy stolen goods, not a pen for your cattle) to buy your stolen goods and they have relatively low maximum cash until the TG quests are complete. You can do this with only one fence, but it will be time consuming and use even more of your own gold.
When you sell an item to a fence, it "cleans" it. That's how a real fence makes money; they buy things for less than value from an unscrupulous source, then resell for under retail or even above if it's a high-demand item. This means selling each of your items to the fence, then buying it back. That's going to get really expensive quickly, as they will always sell it to you for much more than what you sold it to them. You also have their limited gold to deal with, so if you don't have enough gold to inflate their gold on hand by buying up the rest of the store first, you're going to get a lot of warnings that they don't have enough cash to buy the item and that you'll take a huge loss.
This takes a few thousand gold for some items. Tens of thousands if you've been reforging everything to Legendary. If you were on PC, I'd say use the console (item code for Gold Coins/Septims is F) to get the cash, but if you were on PC, you would likely be fixing this by just giving yourself all of the items that were flagged stolen using the additem command and ditching the dirty copies.
If you're playing vanilla Skyrim/SSE, you can put your stolen items into a container owned by someone else that you've done their favor and if they let you take low value items from that container, the targeted action is "search" instead of "steal from". Then ask a follower to "take all" from that container and every item's stolen flag will be removed, including items the owners originally don't let you take.