Before trading again make sure that:

1. You have set your current public trade offer URL. If you created a new URL you need to update it by clicking here.
2. The items are tradable and craftable (except for the accepted not craftable ones)
3. Your backpack isn't full or overfilled
4. Your backpack isn't outdated, you will have to close TF2 or restart Steam in order to update it.
5. The homepage confirms that TF2 API and/or GC are up
6. You don't have not tradable metal in your backpack, if you do then you will have to remove it
7. You have enough metal to pay/items
8. The bot is up
9. You haven't recently changed your password, cleared cache and cookies or recently activated SteamGuard. If you have done any of that, then you will have to wait a week - a month in order to be able to trade again
10. There isn't any announcement about it. If there is then you will have to read it.
11. The site isn't down