When you reclaim a fortress, all preexisting items will be scattered and forbidden for use by your dwarves (buildings will also be forbidden). This is useful because mature fortresses may have tonnes of items, and by the time your dwarves finish picking them up, you would have spent a year hauling everything inside.
The solution is simple: designate all "wanted" items to claim. The combination is the following
Then select all items you want to reclaim within the rectangle. You could also do this manually (with k) or within the stocks menu, however manually is only good for a small amount of items and to use the stocks menu you need to setup a bookkeeper and have him do enough work such that every item is accounted for (which will take time).
It is possible to use DFHack to prevent item scatter altogether. The command is called
lair and when used marks the current embark as a "monster lair", therefore preventing item scatter on reclaim. Note that you need to call this before you abandon the embark that you want to reclaim.
In the abnormal case where bins were being used before the reclaim (which would render them unusable on the reclaim), there is no clear indication that distinguishes those "bad bins" from the good bins, apart from the fact they aren't being used. According to some information on this 2009 post, simply moving them is enough to reactivate them.
Due to the factors involved, dwarves will not move those bins. Hence, the use of the
autodump feature of DFHack might prove handy, as it should move and "repair" the bins for usage.