Error message during download

Often when I try to download something (new Quicktime version) part way through the download there is an error message asking to shut down the computer. This seems to happen only when I try to download bigger files.

We need the recent Quicktime so we can install iWorks.

Any suggestions?

Thanks,
Juli

 

Not sure of the model. It's a macbook bought in 2008 running OS X 10.5.6.
I called support and they showed me how to reset it (take out battery, option, command, P, R), but that didn't work. Their second suggestion was to "active install." Can that be done with OS X 10.6.1 disc (we just bought a new mac) rather than the old install disc?

Thanks for trying to help.