Help Old Dolphin moves 10' back and forth

by Michael
(New Palestine)

So, my dad gave me his old dolphin, he lost his power supply so I bought a new one. Starts up and runs like a champ, but it just goes like back and forth, it really doesn't vary from its 10' back and forth, and it doesn't suck up very much stuff. Could a bag need to be replaced? Bad logic board? I don't have a remote, so I am thinking that would have been a good thing to try but I just don't want to dump 7-800 in a machine that is older.