Which version of the tools are you using and in which editor are you editing the symbol? Is this a block symbol on the sheet or a library symbol? You will probably get a quicker answer by contacting customer support rather than this forum.
I am using PADS9.0 and it is a library symbol.
Check the 'selection buttons' in the toolbar to see if you have switched off the selection of any objects.
Have you contacted Customer Support?
Thnaks, I have resolved my issue thru Mentor tech support