if you have too many items to be able to open any boxes, there really isnt anything you can do. the developers locked down old players' accounts
i don't think he is able to get any new items if he has more than 100 items, unless he buys more item space or uses the legacy convertor to make the old items into the power cell things, but those things take up space as well. and its not possible to choose what you want to convert into power cells. it just converts all the items of whichever class you choose. i was trying to only convert my weapons and mech bodies and legs into power cells but it did everything. so i lost all my good items like 1kg teleport and such.