What version of AutoCAD are you using?
From the AutoCAD 2004 Help file:
"You can select groups by name at the Select Objects prompt. If the PICKSTYLE system variable is set to 1 or 3 and you select any member of a selectable group, AutoCAD selects all group members that meet the selection criteria. You can also toggle group selection on and off by pressing CTRL+H or SHIFT+CTRL+A."
Controls the use of group selection and associative hatch selection.
0 No group selection or associative hatch selection
1 Group selection
2 Associative hatch selection
3 Group selection and associative hatch selection
By the way, have you checked to see what the system variable Edgemode is set to?
Controls how the TRIM and EXTEND commands determine cutting and boundary edges.
0 Uses the selected edge without an extension
1 Extends or trims the selected object to an imaginary extension of the cutting or boundary edge
All this information can be found using AutoCAD's Help.