Actually, I think it is indicating that it is mad, not 100% sure.
Try looking at the amount of hears/happiness it has. If they're low, fill them up.
If your Tama is sick, repair it.
Then try using the computer.
Otherwise, give it a little break then try again. If it doesnt work form that, I'd say it means you can only use the computer if your an adult (if you aren't already an adult)
//Haze