Sounds to me like a heat issue. Do you have a small fan you can run on low and point the airflow across the bottom of the machine as it runs? I'd test that and see if it helps.

[quote|Sarabian]Sounds to me like a heat issue. Do you have a small fan you can run on low and point the airflow across the bottom of the machine as it runs? I'd test that and see if it helps.[/quote]

Your iBook knows when it's getting too hot and it wont let you continue what your doing if it is. Sarabian raises a valid point in the short term. In the long term you should replace your fan and your heat sink: both are available on ifixit.com. This is an odd problem but as iBooks are quite old now, it's important to replace the occasional part to keep the system fresh.

[quote|QEIIRepair]Your iBook knows when it's getting too hot and it wont let you continue what your doing if it is. Sarabian raises a valid point in the short term. In the long term you should replace your fan and your heat sink: both are available on ifixit.com. This is an odd problem but as iBooks are quite old now, it's important to replace the occasional part to keep the system fresh.[/quote]

Thank you both - I haven't successfully tested a fan-assisted work-out, fans not being essential household items for the British climate. iStat Nano widget tells me that the fan is running at 0rpm though I don't know if that is the norm for G4 iBooks when running normally. The only other piece of info is that the pointer can still be moved via the track-pad after the rest of the screen freezes. And at the last test there was no sign of a temperature spike on iStat. I'll see if I can extend work-time by some form of external cooling, and if that yields results, will go for spare parts option. Many thanks again. GSJ

[quote|gsj4gsj]Thank you both - I haven't successfully tested a fan-assisted work-out, fans not being essential household items for the British climate. iStat Nano widget tells me that the fan is running at 0rpm though I don't know if that is the norm for G4 iBooks when running normally. The only other piece of info is that the pointer can still be moved via the track-pad after the rest of the screen freezes. And at the last test there was no sign of a temperature spike on iStat. I'll see if I can extend work-time by some form of external cooling, and if that yields results, will go for spare parts option. Many thanks again. GSJ[/quote]