Middle drawer on roll top desk (used for keyboard) WILL NOt slide all the way in. Is it hung on something or is this a safety feature?

Many desks have a central drawer-locking function, controlled by the lap drawer. Check to see if there's a mechanism behind the drawer that is hung up---this may prevent the drawer from going the whole way in. Some drawers have an anti-tip feature that will make a drawer SEEM that it won't go in, just requires a little gentle pressure to properly engage. More description or photos of the problem area would help.