Yep, it might be time to pop the cover off that machine and have a (careful) snoop around. If it's been sitting in an attic for years without being turned on, the battery could've started leaking, but it's easy to see if that's the case when you open it up. Capacitors can also fail after a few years, and dead capacitors usually don't do that much damage, but are sometimes hard to spot because they often look like working ones. And, as Bloodline suggested, while you're at it, reseat the ROMs and any other chips in there which might've come loose.
