Thanks VERY much for your replies, Swordmaker. Really appreciate it. I’m going to advise he pop the battery out and clean the contacts, as you suggested. Hopefully that’s the problem and will allow the computer to turn back on again.
However, when he was on the phone with Apple tech. support, they told him to hold in the power button for 10 or 15 seconds (as you suggested as well) in order to power down the machine. Doing this didn’t turn off the machine, unfortunately. That’s why he ended up popping out the battery in the first place.
Thanks again very much for your help. Fingers crossed it’s just the battery and no viruses!
The machine should come on with the battery removed and connected to the power cord. If you do not shut down properly it can take what seems like forever for it to reboot in some cases.