I'm a lazy person.. I had so much stuff and I didn't know where to store them. So I ended up storing them in the barrels near the Warmaiden's. When I checked the barrels after several days, my items were gone... There were daedric artifacts and dragon priest masks. Do barrels reset or something? Why did my items disappear? :'(((( I play on pc.

Most outside and unowned containers reset after a few days. The most time is up to 10 days but it depends on where the container is.

http://www.uesp.net/wiki/Skyrim:Containers

You may have lost all your goodies.

I play on PS3, so I'm not savvy with the console and if there is a way to retrieve them.

Barrels are not a good place to store things. Even in the homes, Barrels can respawn. Furniture is much better as it never respawns.

Here are the locations that don't respawn (I would still avoid the barrels)

http://www.uesp.net/wiki/Category:Skyrim-Places-Safe

Do you have a save slot from before you put stuff in the barrel?

No...Unfortunately I think I lost all my stuff. Including Mehrunes Razor, 5 priest masks and more..(

Disappointing as it is, don't feel too bad. Many of us have learned that lesson the hard way. The Alchemist Shack in the Rift has an end table that is safe storage. I use it sometimes. The end table in Angi's Camp is safe storage as well. Another good tip to remember is that spouse's homes are not safe storage, unlike one might assume.

Ouch! Sorry to hear about this - the dragon priest masks are irreplaceable. Mehrune's Razor is not that great as the killing percentage is so, so, so small. If you are going to use storage that re-sets, just be sure to visit the container more frequently than every 10 days.

I made a similar mistake once but only with firewood. I stored something like 100 pieces inside Fort Dawnguard near the smithing area only to have them disappear. I intentionally waited more than ten in-game days passed between visits so the smithing supplies would reset.

Well if you really want to since your on pc you can use the command console to replace your items. For Mehrune's Razor you would hit the tilde (~) key and type

player.additem 240d2 1

The 240d2 is the item, the 1 following it is how many.

Here is a page that shows the other item id's of your lost loot. http://www.uesp.net/wiki/Skyrim:Items

Typically I don't add items to my character but if I lose them due to a glitch or bug then I have no problems doing so. And one time I started a poor knight character as a playthrough and added Iron armor and a steel sword. But for the most part I think if you just add too many items that takes away from the feeling of accomplishing quests to earn them. But, since there is no way to cheat in a single player game and you earned them, I'd do it