What happened...

...and how do I fix it?

Hi all, I'm new here so apologies if this is covered elsewhere but I'm still finding my way around.

I'm not new to Macs though, been using nothing else for 20 years.... my main machine these days is a G5 iMac with an extra monitor to extend the desktop.

My problem....

For a long time now, I've had the Mac go to 'sleep' when I leave it unattended. I don't switch it off very often as I work at it all hours. Whenever I return to it, I touch the keyboard or move the mouse and it 'wakes up'. Then, once I log in (enter my password) I find everything as I left it and I can carry on working....

At least that's how it was... As far as I know, I haven't changed any settings but about a week ago I started finding that the Mac hadn't gone to sleep. When I returned to it - sometimes after several hours - the screen was on as I'd left it. This was frustrating, annoying and worrying for various reasons, as you can imagine. Since then, I've tried various combinations of settings in System Preferences - Energy Saver, Desktop & Screensaver, Security - and now the Mac does go to 'sleep' but when I wake it, all programmes have closed down (including any that I was working in).....

So, what happened? Has something drastic happened to my Mac? How do I it get back to how it was?

I'd appreciate any help.

Thanks
Cris

ps
BTW, I initially posted this in the wrong forum... I know! I'm sorry...

Welcome to Mac-Forums..

What version of OS X are you running on you iMac and is it up to the latest rev? Now when it's begun working again, are you at the initial login window or just a lock window?

I'm on 10.6.8 but that hasn't changed recently.

When I come back to the Mac, it's running and when I touch keyboard or mouse, the monitors immediately light up to, I guess, the lock window.

If I've only left it a few minutes, it then opens where I left it (I've just discovered) but any length of time and it's back to starting up progs again. No screensaver or wallpaper even - the wallpaper comes back once I enter password...

If you were back to the login prompt after that longer time away, I would think that your Mac has crashed and restarted itself. But then you would not only hear the startup chime, you'd most notably be at the login screen, not a lock screen.