If you can see the beam of light from items but can not see their name, or pick them up, the most likely issue is your loot filter configuration.

To check your current loot filter settings open your inventory and look for a button on the bottom-right of the inventory screen, above your gold count. This will bring up the loot filter. To ensure you can pick up all desired items, check that the appropriate buttons are not greyed out in the filter. If you want to be absolutely sure, you can create a new profile using the '+' button. The new profile's default settings will allow you to pick up everything of every quality.