help please - imac acts as if shut down and running suspiciously slow

Hi All

My imac has recently started behaving peculiarly. I've left it downloading stuff and twice in the last 24 hours, when I've returned, the screen is off, and wont come back on by pressing keys, moving mouse, tapping power button - seems dead. It's still on, but registering nothing on screen. This weirdness has coincided with it running noticeably slow of late.

Am running OS X 10.8.8, it a 2.8Ghz Duo, lots of memory, only 18 months old.

Can anyone help point me in the right direction please?

Thanks

What do yo mean by downloading stuff? Was it a system update? Another software update? You might try to start the Mac using the original DVDs and then run Disk Utility from the DVD to check permissions, etc.

i dont have the discs am afraid, i got it from a 3rd party

downloads have been torrents, so the stuff wasnt updates of any kind

thanks

I'm not knowledgeable about torrents, but our systems analyst at work explained to me that when you download torrents, your computer also serves as an upload machine for others. That could be one reason for the slow down. Do you only see this slowdown at those times? What about if you quit the torrent application and re-start your Mac? Does that make things work normal in terms of speed?