Inspiron 1520 keyboard replacement...help!

Hi.

I have an Inspiron 1520 with Vista Home Premium.  I have recently been having keyboard issues (periods of complete unresponsiveness followed by hyperresponsiveness, repeat).  Telephone technical support believed this to be a hardware problem (backed up by the fact that an external keyboard works perfectly) and they sent me a new replacement keyboard.  I have just tried to replace the keyboard with the new (according to owners manual) and am finding that the new keyboard is not working at all, nor is the old original keyboard.  Also, the controls on the front of the computer (volume, etc) are now unresponsive.  I am wondering if I am not connecting the cable correctly or if there is something more sinister happening.  Has anyone any experience with replacing the keyboard on the Inspiron 1520 and could offer any advice?  I am going to call tech support when I have a couple hours to spend on the phone, but in the meantime would be greatly appreciative of any help with this.

Thanks

Sue