Welcome to the PlayStation Community.
You don't need the original PS3, just sign in with the same account PSN ID & password details you used on the old one.
Customer Service - 1-800-345-SONY (7669)
Account & billing Support -1-877-971-SONY (7669)
Available Mon to Fri 8am - 8pm PST
Live Chat Available Mon-Sat 6am-10pm PST & Sun 6am-8pm PST
Yeah, try this link & you should able to deactivate your account. Mind, it'll deactivate the account on all PS3 systems but then you can just set it back up on the PS3 your currently using.
It might bring you to the home page (not sure), if does just Sign In & go to Account (top of the page) & then look for an option on the left-hand side of the page called Media & Devices. You should see the option to deactivate your account on that page. Hope that helps.