Wow! I remember I got a Roboraptor in 2005 and I used to absolutely love it. I even remember bringing it into school with me a few times, but at that age I loved basically any robot I could get ahold of.
I just pulled my old Roboraptor out of the attic, but he isn't responding at all, so I'll replace his batteries and see what reaction I get from him. I don't really remember what the normal behavior from these guys is, but I'l get some fresh batteries for mine and his remote and test him out to see if I can figure anything that might be helpful to you.
Edit:
I just ran mine for about half an hour after replacing his batteries. At first when I started mine up, he didn't do much unless something moved in front of him in which case he'd roar and walk toward it and sometimes seemed to explore a little bit before stopping. However, I when left him alone for a bit, he started exploring on his own for about five minutes. He does seem to freeze every now and then (go into a mode where he'll only respond to being petted and sensing motion), but seems to snap out of it after 5-10 minutes or so. He'll also play tug-of-war if I put my hand in his mouth. The bad news is that the remote which I thought was his actually belongs to my Roboreptile, so it seems his remote is missing and I can't test the normal reactions to the remote. I'm not sure what is wrong with yours, but maybe if you leave him alone for 5-10 minutes, he might switch modes and become active and more responsive. You should see if he'll respond to any of the touch sensors as well. Also, I know this is an obvious solution and you've probably already done so, but if you haven't replaced the batteries in both the robot and its remote, it would be a good idea to do so. Hopefully yours isn't broken and you can figure out what the issue is!